If it were me I would permanently mount the heater. It could be a simple install to a cabinet door much like these GOOGLE IMAGES...


This install includes flexible propane connections as well as an exhaust tube going to the outside wall...
As you can see this would not take up much of your precious room inside the Fifth Wheel...
Being portable like you are suggesting I don't think will have an exhaust to the outside that you really need to have... Connecting up a PVC type exhaust venting system sitting out in the open hallway like shown in this google image sure would not be to my liking.

These type heaters are very dangerous in concealed locations requiring not only the need for oxygen is absolute but any Carbon Monoxide removed. Certainly don't want to wake up dead...
Just food for thought presented here - thinking out loud only...
Roy Ken