I installed 3 permanent recessed electric heaters in our 29' TT totaling 2000 watts (on 30 amp service). Made my own demand controller and have never tripped a breaker. Good down to about 3C/38F. Works great! Never have to use the furnace anymore.
Best thing about the electric heat is that it's waaay quieter than the furnace and don't have to crank up the TV.
Sure glad we live in the banana belt of Canada where it rarely gets below freezing... :) Can't fathom what camping in -12C would be like, let alone -24C. Yikes! :E