We have legs on the one we use Ozz. With my camper only having the two slide and (if I remember you have a 3400) your extra slides I'd move up one size on the heater. We use the forced air heater to bring the camper up to temp. and then the blue flame works fine.
This is close to what I have
http://www.amazon.com/Mr-Heater-Prop...6258986&sr=8-5
Ours has a thermostat not sure the one at Amazon does.