I got a Coleman Black Cat, a wee catalytic heater that runs on propane. Apparently it’s safe indoors, as long as it has a bit of fresh air, which it does (I always leave the front windows open a crack), and as long as the heat surface isn’t touching any combustibles. I’m not very happy about the fact that it uses non-refillable tanks (they are recyclable), but I’m very very happy with the cozy warm blast it puts out on cold mornings! A tank only lasts 7 hours, so it’s not something I’d leave on at night (and it wouldn’t be safe to sleep with it on anyway), but 15 minutes is enough to make the van comfortable for getting up and changing clothes, hanging out for a while. I don’t know if it’ll really help with the moisture issue; I expect that’ll be an ongoing struggle.