[font=verdana, geneva, lucida,]We carry a portable Buddy Heater and Patio Heaters as a backup in our Sprinter motorhome. It's supposed to be safe indoors, but I wouldn't want to fall asleep with it on so we'd probably only use it for a before-bed heat up, maybe a 2:30 am refresh, and then a morning warmup.[/font]
[font=verdana, geneva, lucida,]When I used to do a lot of winter climbing and skiing, we'd often fire up a stove inside the tent. We knew it was unsafe, but sometimes all you care about is getting warm. That reminds me. The Buddy Heater's oxygen sensor will kick in at altitude. They say 7,000' maximum, but we've used ours at about 9,000'. And Icarus is right about the moisture. Burning a gallon of propane produces almost a gallon of water. Of course, it's in the form of vapor so that gallon of water will be evenly distributed over the cold surfaces on the interior of your van.[/font]
[font=verdana, geneva, lucida,]You should definitely have the alarms if you're doing any cooking inside the van but Buddy Heaters have a low-oxygen shutoff, burn almost 100% efficiently, and have a tip-over shutoff. There aren't very many heaters rated for indoor use like this one is, but still... you roll the dice and you take your chances.[/font]
[font=verdana, geneva, lucida,]Insulating is an easy way to reduce your need for heat. By making the sleeping compartment as small and well insulated as possible (being mindful of having ventilation for breathing), you can almost get by with just body heat. Add a winter sleeping bag to the mix and you won't need your buddy heater during the night.[/font]