Hi Mark; Is this an RV that is stationary ? Or does it travel frequently ?
Even a bell heater has a fair amount of weight to it. A regular mass would be just too heavy to travel with.
Directly over the rear axle and centered a small brick bell J tube might be about the right size. The chimney would have to go thru threw the roof though. You certainly could only burn while stationary. It would affect mileage with the extra weight.
All in all if it is a moving vehicle it's doable but
should you??? In my opinion if this is a stationary RV then go for it, if you drive it a tiny amount then OK, but if you travel much ... maybe... a kerosun heater or a small propane heater might be a more convenient method to stay warm.
If you do build a
RMH and you were to try to drive down the road while lit... THEN you might have a VIKING CREMATION VEHICLE !