Is it cheaper to heat my RV on propane or electric?

Cost difference is small, but convenience factor makes a difference. I use both, but because of convenience, I use electric more during times when it is above freezing. However, when the temp goes down below freezing, I use propane more in order to keep the basement warm, to prevent pipes there from freezing. Electric heaters don't heat the basement.

By using a combination of both, it makes my propane last longer.