bka0721 - I love hearing about folks full-timing in small RVs. I know of one couple full-timing in a truck camper (for 2+ years)... You're only the 2nd truck camper full-timer I know of. How totally cool is that?! How many years have you been living in your truck camper??
I'm sorry your Wave heater doesn't work above 55 degrees or below 25 degrees. Other people I've met with Wave heaters have found they work really well in a much bigger range of temps. They are the oldest of the vent-free heaters on the market and have a really long history with RVers (some 20+ years).
Ours is a blue flame heater (the newest type of vent-free heater), and we turn it on when the inside temp gets below 75 (sometimes we hold out til it's below 70). It works really well when outside temps are in the twenties. We haven't been in anything below about 20 degrees though.
Usually our fifth wheel stays about 10-15 degrees above outside temps overnight if we don't run the furnace or vent-free heater.
Maybe your heater is too small? (Hard to imagine in a truck camper, but who knows?!). Our blue flame is a 20,000 btu unit (we heat about 350 square feet of space) and we rarely run it at more than about 20% of it's full-on capacity.
Our unit works fine in any temperature and hasn't given us any trouble since we installed it in 2008.
More about it here.