the one out of the caravan will be better.
caravan club sell them as do southampton calor.
The l5 auto ignites, the one you'll be getting has a pilot light, don't worry this is better.
If you can take the di off the van thats good, and put a t piece and the a tap going back to the tank after the heater and before the reel.This gives you lots of options that you'll thank me for later. The heater in the caravan is probably a morco or a rinnai, find out. Both are good.
It's possible you may have to cut a hole in the roof, if you don't want to use an 4"aluminium hose fed out the door.