I believe the general consensus is if you are using the propane furnace and blower it will be one battery - one night...
We have not had good luck using the propane furnace as it is always way too hot for us in our OFF-ROAD POPUP camper and of course consumes our battery power big time to run the 5-6AMP very loud blower fan all night.
I don't know if I would use the catalytic type propane heaters or not in a close area like the Truck Camper. You would definitely have to open so vents somewhere to be safe which defeats the purpose of heating in the first place.
I use a MR BUDDY heater in my OFF-ROAD POPUP Camper and it sits right under the fantastic fan which is cracked open about an inch.
Alot of guys have had great luck with the CAT 5 type vented propane wall heater.
Consider these two photos from GOOGLE IMAGES on how this one RV guy mounted his.
I also think the TRUCK CAMPER would be an ideal candidate for the HYDRONIC TYPE water heater unit much like this concept...
I am wanting to test out this concept using the hot water heater for heat source... A couple of guys have had great success doing this
The heat registers could also be the wall mounted base board panels
One full time RV'er on here actually has found in-floor mounted heat registers which sounds very promising for hydronic heat.
food for thought
Roy Ken