Cheap Heat has some very specific requirements and high amperage requirements. You need 50 amp service at a minimum and some special wiring is required.
If you use electric heat inside, you can also use electric heat outside. We use a couple of 100W light bulbs in the wet bay and where any plumbing exists. There are also some really nice, really small 250W electric heaters that will do the job and circulate the air as well. If you plan on "seriously cold" camping you might need the propane and the electric heat to keep your plumbing safe but in most 20's - 30's camping, most class A's will do just find with a bit of supplemental heat.