I don't know the size of your fifth wheel, so this may or may not apply. I own a 23 foot fifth wheel that has a half-height fifth wheel bedroom. It is small. I use two electric heaters exclusively to heat it. I use a radiant type heater with fan forced air for the larger compartment. In the bedroom area, I use a small utility heater. Both are UL Listed (very important for equipment like this). Both have two ratings. The smaller one has 750 watts and 1500. The larger one has 1000 watts and 1500. I use the small one set to 750 and change the other one as necessary. I have 30A, and they work in this configuration.
If I turn both to 1500, though, I pop the breaker for my receptacles. I am currently looking into wiring one into the same circuit as my air conditioner so that it can be off by itself. Both heaters cost less than 40 dollars (Wal-Mart). They work great, but you have to keep safety in mind with these heaters. You have to be able to set them up three feet from anything and make sure nothing is going to leak/spill on them. These heaters will start fires very easily if left unattended with obstructions or whatnot, so use with care. I live in my trailer by myself, so I don't have any pets/kids to worry about getting burned on my heaters, which is another consideration.
Wattage is not the only consideration, though. Design has a lot to do with it. I do not have a whole lot of volume to keep warm, so I didn't need anything fancy. The local shelf at Wal-Mart has everything from the cheap heaters I bought (that work very will with some noticeable background noise) to a whisper quiet ceramic one that sits in a metal cradle and sends heat 360 degrees and has a remote control.
My main reason for the electric heat is that my furnace eats propane like candy, so I use the electric so I do not get stuck trying to switch tanks in the middle of the freezing cold night.
Hope that helps, and be safe!
1994 Chevy K2500 Cheyenne
1984 Great Divide Fifth Wheel 23'
Using a fithwheel to gooseneck adapter.