I fix these things.
1.Single? ok to live in.
2.Stinking hot in summer.
3 If in country, can be prone to vermin damage inside, mice etc.
4. Anything previous 2000 date in age, likely to leak from rooflights,doors etc. due to sealent mastic going hard, so water can get past.Also same problems can occur with silicone sealed models in newer vans, usually caused by poor manufacturing, or rough transporting, or rough handling when site-ing.
5.Annoying drafts from permanent fixed (Legal Reqirement) vents, floor and upper ones.
Seen these taped over etc, can cause gas appliances to not burn correctly, flue's not to perate correctly when covered.
6.Winter living in all vans are generally crap. Think statics as a tin box in the middle of the field !
Frost damage biggest problem, blown pipes fittings, appliances blow to bits!
You can have c/heating on full blast inside, but water pipes outside can and will freeze solid if temp keeps around -5 degree or worse for 12 hrs say.
When water freezes, it cant be compressed, air can though !
So what happens is frozen water freezes, compresses air in the water, this gets forces up to hundreds of punds per square inch!
These forces is what blows fittings apart, splits tap blocks, splits shower valves, and also blows centra heating boiler/water heater components apart !
7. That covers a few probs , have fun!!!