Is the trailer 30 or 50A? What "breaker" tripped; inside the trailer or the one at the power ped feeding the trailer? Do you have an EMS in use, if so what does it say on the incoming power? If the gfci won't reset it tells you that there is probably no power coming to it (it won't reset unless there is voltage there) and one side of the trailer with no power says you possibly lost one leg of a two leg 50A circuit. Your furnace, thermostat and control board operate on DC current not AC. If your batteries haven't been charged by the converter due to loss of that leg of power they won't operate the furnace etc. You need to do some further analysis on what your incoming electrical looks like. Do you have a VOM and know how to use it? They are invaluable.
Danny and Susan, wife of 56 years
2019 Ram 3500 Laramie CC SWB SB 6.4 4x4 4.10
2020 Montana High Country 331RL