I replied to your other thread, am close but not close enough--plan to take the Boler to Canada but not until next spring I imagine.
Am happy to share ideas/progress, but am a newbie like you. I have learned so much reading these forums and keeping lists of ideas/suggestions/plans. It is fun and also overwhelming, especially when you bang your head on stuff, which I did this morning and is why I am not cleaning the Boler as I planned today. Instead I am reading on here and icing what looks to be a nice size bruise.
The PO (previous owner) of mine converted the rear couch into a permanent bed, so I ordered a full size memory foam mattress and plan to cut it down to size (with a serrated kitchen knife, or an electric knife if I can get my hands on a used one). I am dreaming of ways to change his structure for the bed support as it is, in my opinion, crappy. Especially since it gave me the bruise I mentioned above.
There are a number of folks who have posted about replacing their floors. Mine appears good and I'm glad because that is way above my pay grade. But it is doable, and you can learn about it on this site!
Do some research on foam types before you decide what to go with for cushions. I am putting that off for a winter project.
For a furnace
alternative you might consider an electric space heater. If you will be camping at sites with electric you could wait on the furnace for a bit and see if you'll want to replace it or not.