I know of several vented heater setups that will work for off road camping. These are more for cargo trailers, but I think they might work in some of the larger teardrops too. The rv furnace would be fairly easy to squeeze into a td camper since it needs very little clearance room.
One is the Dickinson line of boat heaters. They use very little floor space, heat well, are quiet, and use either no battery or very little depending on if you turn the small fan on. Here is a store link to some of them: http://www.go2marine.com/search.do?q=di ... ch_button=
Here is a thread on the propane Dickinson installed in a 6x12 cargo trailer.
viewtopic.php?f=42&t=56858
Great stove.
Another is a 12,000 btu rv furnace such as the Atwood Everest Star 8012. The small ones like this use less battery power than the bigger ones, but it still does use about 2 amp hours. It also needs to be permanently installed which either takes up floor space if you haul bikes, or it can be installed on a lower shelf. There is still the fan cycling noise problem that many with rv furnaces complain of. Here is an example from one store:
http://www.adventurerv.net/atwood-evere ... -8605.html
Here is one installed in a 5x8 cargo: viewtopic.php?f=42&t=33848&p=608475#p608475
Another is a Nuway 2000 propane stove: http://www.nuwaystove.com/model2000.php
Which is also used in large tents.
No fan use, but does take up floor space. It can be permanently installed or can be installed as removable for hauling. It does use cabin air for combustion so a small vent should be open. (vent should be open anyway for condensation etc) Here is one installed (look about halfway down the page) viewtopic.php?f=42&t=55219&start=45
Hope these help.