Second thought, usually: Did I do something wrong?

Here's the truth that no one tells you when you're buying your first caravan or hybrid camper: every single van, every brand, every price point — they all do this. From a $20k camper trailer to a $200k full-rig European caravan. If it's got people sleeping in it overnight, it's going to deal with condensation. And it has nothing to do with a fault in your van.

The numbers nobody mentions

Two people sleeping in a caravan release over a litre of moisture into the air overnight through breathing and body heat alone. Add a family of four and you're closer to two litres before anyone's even put the kettle on. Cooking a single meal evaporates around 250mL of water into the cabin. Boiling a kettle for a coffee? Add more. A hot shower (if your van has one) puts another 1.7L of water vapour into the air.

That moisture has to go somewhere. And in a sealed, insulated cabin sitting in cold air at 3am, it's going to find the coldest surface it can — your windows, your aluminium roof, the canvas wall against your bed — and turn back into water.

This is basic physics. Not a defect. Not a warranty issue. Just what happens when warm humid air meets a cold surface — same reason a cold beer "sweats" on a hot day.

Why hybrids and pop-tops feel it more

A hybrid camper or pop-top sits in a slightly different spot to a full hard-walled caravan. You've got more surface area exposed to the cold (canvas walls, pop-top sections), and those surfaces are usually thinner and colder than a fully insulated wall. The junction where the canvas meets the hard roof or floor is often the first place you'll see moisture pooling.

You're not imagining it. Hybrids do show condensation more visibly. They also dry out faster once you ventilate them properly — which is good news.

About that square above your door

If you've spotted a perfectly square patch of condensation forming above the door — almost too neat to be natural — you're not imagining it, and you haven't got a leak.

Every Mars caravan and hybrid is built with a pre-installed metal frame above the door, ready for owners who want to add a dust reduction unit down the track. It's a small thing we do at build that saves you cutting into the van later if you decide you want one. The trade-off is that metal conducts cold far more efficiently than the surrounding insulated wall — so on a chilly morning, the exact shape of that frame shows up as a square of condensation while the rest of the wall stays dry.

Same physics as the rest of this article — a cold surface meeting warm humid air. The square is just the frame making itself visible. It's not a leak, not a defect, and not something that needs fixing. Ventilate, wipe it down, and treat it the same as any other cold spot in the van.

How to beat it when you're using the van

Ventilate, even when it's cold. This is the one most people get wrong. Sealing the van up tight to stay warm actually traps every bit of moisture you're producing. Crack a window. Pop a roof vent. Even a 1cm gap on opposite sides of the van will let humid air escape. You'll be amazed at the difference by morning.

Cook outside whenever you can. The slide-out kitchen exists for a reason. Boiling water, frying breakfast, even toasting bread inside dumps moisture straight into the cabin. If the weather's foul, use the rangehood and open a window.

Run a diesel heater if you've got one. Diesel and gas heaters produce dry heat that actively reduces humidity in the cabin. They're a game-changer for cold-weather camping. (Note: unflued portable gas heaters do the opposite — they add moisture. Don't use them.)

Use moisture absorbers. A couple of Damp Rid tubs or similar from Coles, Bunnings, or Woolies — cheap, simple, and they pull a surprising amount of water out of the air. Replace them every trip.

Wipe down in the morning. A microfibre cloth across the windows, around the canvas-to-roof seal, and any visible damp spots takes two minutes and stops moisture sitting long enough to cause issues.

Don't dry wet gear inside. Wet towels, swimmers, hiking boots, fishing gear — keep them in the awning or under a tarp. Drying clothes inside the van is the single biggest avoidable cause of bad condensation overnight.

Air the canvas before you pack down. This is the big one. If you pack away a wet pop-top or hybrid camper, you're sealing moisture in for days or weeks. Open everything up, let the sun and wind get to it, even if it means an extra 30 minutes before you hit the road. If you absolutely have to pack wet, set it up again at home and dry it out properly within 24-48 hours. This is the single best thing you can do to protect your van long-term.

"But mine does it when no one's even in it"

This one trips a lot of owners up. You open the van after it's been sitting in storage for two weeks, and there's moisture on the windows, dampness in the cupboards, or worse — a musty smell coming off the mattresses. No people, no cooking, no showers. So what gives?

The answer is the same physics, just running on a slower clock.

Temperature swings drive it. A caravan parked outside heats up dramatically during the day — the aluminium roof can hit 50°C in summer sun. The air inside heats with it, and warm air holds more moisture. When the sun goes down and the temperature drops 20+ degrees overnight, that moisture condenses on the now-cold surfaces. Wash, rinse, repeat — every day, even if no one's been near the van.

Ambient humidity is enough. Australian air on any given day carries a fair bit of moisture, and coastal trips even more. Seal a van up with that humid air inside and the daily heating-cooling cycle does the rest.

Your van's materials are constantly breathing. Timber, upholstery, mattresses, foam cushions — they all absorb and release moisture as temperature and humidity change. A stored van with no airflow just cycles that moisture around inside itself.

Ground moisture creeps in. If the van's parked on grass, dirt, or even directly on concrete, moisture from the ground can find its way up through the floor and underbody. Worse if you've stored over winter or through a wet stretch.

How to keep your van dry in storage

Pack it dry. This is the big one. If you've packed away with any wet canvas, damp gear, or a still-warm fridge, you've sealed the problem in. Set up at home and properly air everything out within 48 hours of getting back.

Crack a roof vent. Even sitting unused, your van needs airflow. Leave at least one vent slightly open — there are vent covers designed exactly for this so rain can't get in. Some owners fit small solar-powered vent fans that run quietly all day during storage. Worth every dollar.

Use moisture absorbers. Two or three Damp Rid tubs (or similar) placed around the van — one in the main cabin, one in a cupboard, one near the bed — will pull moisture out of the air constantly. Check and replace them monthly. Cheap insurance.

Lift the mattress, open the cupboards. Before you lock up, prop the mattress on its side or lift one end with a block. Open cupboard doors. Pull bench cushions away from walls. Anywhere air can't move is where mould will eventually start.

Store under cover where you can. A quality van cover, a carport, or a shed massively reduces the daily temperature swing that drives condensation. If you're storing outside uncovered, a breathable van cover is a solid investment. Cheap plastic tarps actually make it worse — they trap moisture against the van.

Don't park on grass or dirt long-term. Concrete or pavers are far better. If you've got no choice, a ground sheet underneath helps.

Air it every few weeks. A 30-minute "doors open, windows open, vents open" session every couple of weeks during storage makes a huge difference. Combine it with a quick inspection — easier to catch a problem early than discover a mouldy mattress after three months.

Soft furnishings come home with you. Doonas, pillows, spare bedding — bring them inside. They're the first things to absorb moisture and the first things to grow mould. Your van will thank you, and so will your nose.

Condensation or a leak?

One important distinction: condensation is not a leak. If you're seeing moisture only on the inside of cold surfaces (windows, aluminium framing, roof panels), with no obvious source or tracking pattern, that's condensation behaving exactly as physics says it should.

A real leak shows up differently — water stains spreading from a fixed point, damp insulation in one area, drips during heavy rain. If you're ever unsure, send us a photo. We'd rather have a look and confirm it's normal than have an owner worrying about it.

The bottom line

Condensation is part of caravanning. Always has been. It's not a sign your van is faulty, leaking, or poorly built — it's a sign there are humans inside it, doing what humans do (and physics doing what physics does, even when there aren't). Manage it with airflow, smart cooking, and a quick wipe-down when you're using the van. Store it dry, ventilated, and covered when you're not. Do those things and condensation becomes a minor part of caravan life rather than something that ruins a weekend away — or a mattress.

Now get out there.