I got criticized for suggesting this last year, but I'm going to repeat it again anyway. One of the easiest and fastest ways we've found to heat the camper, even better than the furnace or electric space heaters, is to simply turn on the 3 burners on the propane stove top. Your camper will heat up in no time.
If using the stove top for heat is so WRONG, then it's WRONG to use it for cooking also. Now, folks will criticize because it produces condensation, and it probably does. But the fact is ... if you are freezing, it works!
I would NEVER suggest sleeping with the gas stove lit. Don't do that while sleeping. But during the time you are in the camper, and right there, it's a fantastic heat source!
The other option, if you want to be a bit safer, is to turn the oven on and leave the door open. This will also generate a BUNCH of heat! It's great in a pinch, and great when the camper is bone cold. Once the camper warms up, then we turn the stove and oven off, furnace will keep up just fine then.
There again, if this is unsafe because of fumes, or whatever, then the stove is unsafe to use for anything ... including cooking! Be smart, it's still an open flame.