I bought my van used with a propane system and no heater. After way too many hours searching the net I finally found my solution.
I'm too cheap to go with the diesel heater, and was trying to avoid the furnace option. This is a catalytic heater that is different from all the others out there because it is fresh air vented. Really cool system, uses very little power or propane, fully automatic, and produces wonderful radiant heat.
The down side is that they are rather large. I'll be buying the 3000 btu model and installing it on the front side of the side door cabinet. It will face right into the front passenger seat when it's turned around. I'm sure this will become the best seat in the house on a cold day. I know 3000 btu's isn't much, but should be fine in our RB full of people and dogs.
If you want one they are around $450 (3000btu) and he builds them per order so there is a 4 to 6 week waiting period.