FYI,
This is not exactly a heater "alternative", but I opted not to get the FWC heater so I could have additional storage space in the cabinets. Except for cold weather camping, this works great. So, as a FWC installed heater alternative, some time ago I started using the "indoor safe" portable heater from Mr. Heater. For most situations it has worked very well for me. It also sits out of the way nicely up on top of the back/rear cabinet.
I just got back from a cold weather trip over the Thanksgiving weekend, and the one problem I have had with the Mr Heater occurred again. That is if you need to constantly run the heater, it goes through a 1 lb. propane bottle in 5-6 hours. So after falling asleep with it on while it was nice and comfortable (and not being completely inside my sleeping bag), I awoke to being very cold. This is quickly resolved by getting out of your bag, climbing down out of the top bed and changing out the spent bottle and putting in a fresh one. However, it is inconvenient.
A friend of mine showed me a good solution. My Heater's portable heaters can be connected to a larger propane tank. All you need is the propane filter for the Mr Heater, and a propane extension to run from the propane tank. My FWC Hawk model comes with two 10lb. tanks. So its very easy to bring one inside for the Mr Heater, and leave the other one connected for the indoor stove top.
For safety, you have the fact that the Mr Heater is "indoor safe", and comes with a low oxygen sensor that will kick off the heater. You also have the propane sensor/alarm in the camper. I then also slightly crack open a couple of windows for added safety (actually it might be needed, I've had the Mr Heater click off a couple of times and found that having ventilation prevents it from kicking off, I presume this is the low oxygen sensor).
I've got pictures if anyone is interested. This is my first post so I don't know how to add pics yet.
Later,
Willie