We have a small RV too - 24 foot Class C and are currently on a multi-week camping trip in the North East/Central East U.S.. During this trip we are beginning to see many nights in the mid/high 30's and when on hookups our small 1500 watt (5000 BTU) electric space heater will keep the living space interior comfortable (with the cab area blocked off from the main living area).
I believe that A/C Heat strips are about 1500 watts (5000 BTU) too. A couple of negatives to them are that the A/C fan that distributes the heat from them is louder than the fan in a space heater of the same capacity, and the heat from the A/C ducts is coming out high in the coach area instead of down low where heating of the air is most effective - as it does with a space heater sitting on the floor aimed horizontally or slightly upwards.
Other than those two negatives, A/C heating strips are a convenient way to get around 1500 watts of heating into an RV without a space heater taking up floor space.
