gunnix said:
I'll do the polystyrene on the underside of the caravan!
I already heard that from a few people, my girls mother even got tuberculosis from living in a caravan for two years! Although she often exaggerates.
Not lived in a caravan but thinking about the physics of it.
I'd have thought the roof was more important to insulate somehow rather than the floor, it will probably depend on what materials they're made off.
Even throwing a tarp over an uninsulated metal the roof will cut the rate of heat loss by cutting the amount of wind, preferably with something to raise it from actually touching the roof, if you've got acess to cheap polystyrene it might be worth lashing some down then lashing a tarp ontop to stop water build up in the gaps. How about a small tripod support in the centre and a tarp on ridge lines down to each corner, should give a bit of wind deflection that way, and lashed down in as many places as practicle.
Plastic over the windows will only really help much if you can stop the palstic sagging onto the glass. One trick I used to use to do this an unheated house I lived in was to tape it down all round then run a hairdryer over it to shrink the plastic till it was very taught. Doing it on the outside would help too ( it's the trapped air that provided the insulation ) but would probably be prone to blowing off and having to be redone after strong winds.
The condensation on the windows should be cut down this way because the damp air will not have quite such a cold surface to condense on. A possible downside is that they're might be more humidity in the air in the caravan and your belongings will probably be that bit damper.
If your thinking about electric heating then I'd actually think seriously about getting a small electric dehumidifier. This may sound counterintuitive as they use a cooling system to condense the water out of the air if you think about it further, they run at a couple of hundred watts and as it's essentially a sealed enviroment that means your getting that as heating while it's in use while at the same time taking moisture out of the air. The major downside might be that they can be a bit annoying in small spaces because of the noise of the fans.
On the tuberculosis side, don't forget that tuberculosisis a contagious disease, you have to catch it from someone who already has it. The reason it's associated with damp is that the organism that causes it needs the moisture to survive, cold damp conditions generally cause people to chatch colds and chills more easily, when they cough the organism is expelled in the small water droplets, and that other people in close proximity will breathe those dropplets in, putting themselves at rick of catching it. I don't think your self and your ladyfriend will need to worry too much your inside activities in regards to tuberculosis unless one of you is at risk from another source or entertain others who may have it in your home.
The damp may cause other respitory problems but if it's damp enough to cause mildew or rot then spores in the air could cause problems. I suspect that's far more likely than TB unless there's already a TB problem in your area.
One idea you might like to try is if your both going to be out all day, as the van is likelt to be completely cooled by the time your home anyway, open the doors/windows 10 minutes or so before you actually leave each time to air the place.