A 16' Scamp
has a relatively small space to heat, but then there is also little insulation there.
The Fastar is rated about 80,000 BTU or 24 KW.
a 1.5 KW electric heated will do a pretty good job of heating the little camper so I don;t think that the heat output from the heater is a problem.
Now the question is the heat transfer rate from the radiator and water flow.
We are looking for a heat in the trailer of about 70 degrees so a water temp of 102-4 would transfer some heat. Since the water is recirculated and heated to bring it back up to 102 after passing through the heater the second time ??
All I know is that domestic hot water heaters can handle it in apartments.
The reason for the experiment is to determine how best to do it.
If it is below freezing the hot water heater would be drained anyway so it would probably not be used then.
But the if it were running it shouldn't freeze maybe?
I look forward to getting started later.