Kirah,
I've given some thought to where I would mount one of the Propex furnaces. I think that along with a Wave X would be a great combo. Big/easy heat from the furnace and quiet/non-electric heat from the Wave.
Part of the planning is the ducting (or you can have no ducts). I think the best place for "no duct" would be under the stove area alongside the wheelwell (but on the floor). You could set it in there perpedicular to the main hallway and point it straight out into the aisle. There is propane right there already (especially if you eliminate the propane fridge). There is also access through the floor for the exhaust tubes. I think that would be a great, relatively simple install and the heat would come out in a nice, central location (I dislike how the stock heat comes out way up by the cab and then the rear is an iceberg).
(Oh and yes, the combined propane electric model is 220 volts, so not available in the US.)
Another option is obviously where the stock furnace was, but that takes away a nice flat corner location for a "real" chair, a storage chest, a dog crate, or etc. I kinda like having that. Next idea is to put it where the little mini-bar table is on the club lounge, right alongside the wall (i.e. between where the two chairs go). Would take up only minimal foot room. Ducting could then run aft behind the stove with first duct coming out just ahead of the wheelwell (under rear chair base area), and another running back toward the rear hall/bathroom area (little tricky with generator box there).
Possibly it could go under the couch, but then it's like every blooming thing is already there. Still, I think there is room. Not as clear and simple though. But you could potentially run a duct into the bathroom for ultimate decadence (seal with deck plate when showering).
The under stove solution seems most elegant/simple to me. Uses odd shaped space, propane right there, central heat location even without any ducts to take up space or get dirty, relatively easy to run exhaust tubes, not to hard to get electric power to it. And then you have your "minus dinette" space free and clear
Scott: More extended prattle and opinionated blathering, please
BG
PS: I meant to add, that there is also the HS2200 which is for mounting outside. So cool, you could mount it under the rig. Sounds super nifty but after examining it I think I'd go with the inside one. The thing is, it's so small anyway and there is that easy wheelwell space under the stove. The outdoor one you have to run the (biggish) ducts up through the floor and there have been some rodent proofing concerns. Also you need to insulate those ducts. (With the inside mounted furnace, it's the exaust ducts going outside vs. the heat ducts coming in on the outside mounted one.) Also, the outdoor one is only the size equivalent of the smaller blue indoor one (I think around 6,400 btu), whereas the bigger green indoor one is, 9,500 btu. An overly large furnace is not a good thing, but I think the 9,500 btu might be nice in our case. But you could possibly mount the HS2200 under the stove/wheelwell area outside (would need more figuring and I already think I would prefer the 9,500 btu inside mounted one.
Oh, one other thing: You might think, Oh, the outside mounted one will be so quiet! It might be slightly quieter, but the thing is that the most noise is just the air coming through the ducts, from what I understand and so that's pretty much unavoidable with any forced air furnace. The way I would use one is just blast it full on for some time in the morning and then keep things warm with a nice quiet Wave or similar. Re-blast when needed. I'm not one to just have it coming on and off randomly 24/7.