Not that I can think of unless you install a little wood burner and heat with wood or have enough battery capacity to heat that way which would be very expensive.
You the guy with the rusted out LP tank?
Have you considered a storage area in the RV that you could modify to accept 20lb or 30lb portable LP bottles? Basically just needs to be sealed from the interior with open air ventilation. Piping and hoses shouldn't be too much of a challenge.
Another option that would use electricity, but near as much as electric heat could be a pellet stove? Quick check, saw a wall mount pellet stove that was 27x36 x 12" deep. Heats 1000sf, so you could run it very low to heat a couple hundred sf?