I am not sure what you want to do with the TT. Do you want to use it in freezing weather, or just store it in freezing weather? Check your TT manual. All plumbing needs to be winterized when temps drop below 32 deg F.
Pipes, fittings, and valves under the floor are going to suffer freeze damage even if you have heat on inside the TT. PEC tubing can resist freeze damage, but fittings and valve are not likely to survive. If heat is not on, pumps, fittings, valves, and fixtures will all freeze.
Tank heaters in an open underbelly may or may not protect tanks. They will not protect the rest.
It is possible to wrap all pipes and things in heat tape and insulation. This would be a major operation with attention to detail and no slipups. Inside of TT must be heated all the time. All heat tapes must be active all the time. Shore power must be on all the time. Towing at 60 mph may cause freezing even with heat tape and batteries will not last long.
Dutchman Kodiak Cub KD176RD 2018
Nissan Pathfinder 2015