I'm trying to find a small heater that I can mount to the top of my camper shell and run it off of a converter. I like the set up I have for sleeping but it gets dang cold back there sometimes.

 

You're going to be hard pressed to find something electric that will last very long. I have seen a few gas powered heaters made for inside tents and such, those may work.

 

We've been running the coleman tent heaters for a couple years and never had any problems. Minus the hole I burned in the tent floor but that was my fault. I always like leave a couple windows cracked just in case, to get a cross draft. Probably could get a battery operated CO monitor and lock up all the windows.