Your Trailer is brand new, waiting 4 weeks is ludicrous. Maybe a call to Forest River, explain the situation and get a mobile guy to come by and fix it.
I lay odds if it did work at first the fuse bypass trick caused something else to open up. My money is on the thermostat itself. The coleman has a heat anticipator, at least mine does, this is a piece of wire that heats up and moves the spring to stop operation of the mercury switch.
Thread on replacement of thermostat with a digital
Analog Coleman Mach Thermostat