I have spent extensive time parked and with heaters in my camper this
fall/winter and I have determined the following about BTU requirements for
heating a parked Vanagon. These numbers are from memory, but they're
probably a good guide. For the most part, these numbers are with the roof
down or mostly down. If you're going to pop the roof, you need more, obviously.

Outside Temp                  Inside Temp             BTUs

45                                      65-70                            5,000
25                                      45-50                             5,000
20                                      60-65                            10,000
0                                        65-70                            15,000

The upshot is that you want a lot of BTUs. I'd shoot for 10,000 as a
starting point. I have a portable 5,000 in my camper and while it is nice it
really isn't adequate when it gets cold out. I supplement this with a
variety of other heaters I have when it is really cold.

I have tested these with carbon monixide testers a lot too (Home Depot) and
they never set off the alarm though idling the car does.
___________________________________
Derek Drew                           New York, NY
drew@interport.net (main address for e-mail)
derekdrew@aol.com (alternate/backup address, checked infrequently)