Dan,
I understand. Just looking for other options that might help.
Yes, heat tape will work. Heck, just get a short length of 120 v tape at Home Depot, cut the thermostat off, and run it from your inverter. Losses really won't be that much, especially if your inverter is controlled by a timer so it is only on for a couple times a night, for an hour or so at a time. Don't forget to insulate the pipe or all this will be a waste. My experience is that it doesn't get too hot for fex type plumbing.....even when then that plumbing is insulated.
As to your recirculating system, am guessing you just have a valve that you open and close by hand. If so, you could replace that manual valve with one that is controlled by a solenoid (~15.00). Then just use a timer (unknown price as I built my own) to activate it.
Another thought. If I remember correctly, you prefer to save battery power by keeping the inside of your trailer cool (er, cold) at night. Perhaps if you heated the inside of the trailer, maybe even directed some heat into the problem area with a fan, and insulated the pipe, the problem would go away. Yea, I know, the darn furnace draws a lot of power.....much more than heat tape does. So just install a Wave Heater (and an second CO detector). Not only "might" your freezing problem go away, but no more cold noses and toes too.
You can use the thermostat you cut off the heat tape to control a fan (it's just a switch).
