I strongly recommend if you go with a forced air heating system... bite the bullet and go propane. odds are you already carry propane, so one less fuel to worry about (n/a if you have a diesel rig).
@PapaDave has a propane heater and the nice thing is it's reliable at all temps... (I've fought with mine a ton under 20* and have to keep it in my rig and fire it right up as soon as I take it out or I end up with sensor errors) and his cycles on/off to maintain temps... diesels will only go high/low never off... and in a RTT low is all you ever really want. Same Camp, single digit temps in Montana in January Dave was able to maintain 65 in his tent... while I, 30' away was sitting at 70-75 with windows open...(couldn't shut it off because I feared it wouldn't turn back on) fast forward to April, mid 20's at night, Dave still at 65, I was 80 and climbing with all windows open on low, had to shut it off... dropped to 40... turned it back on (thankfully it fired back up) back up to 80 in a few min.
Unfortunately this means I have to plan on my diesel heater NOT working so I can't really bring less bedding (lighter bag)without risking freezing due to sensor failures.
if you're serious about 4 season camping, which I am, propane heat exchanger is the only way to go for an RTT IMO)