Are you saying the fuse on the board is good or the fuse in the trailer panel is good?
If there is a fuse on the board you want to make sure if it is fusing the 110 and not the 12 volts. If you see a fuse on the refg. control board I would take a volt meter set on a scale that will show 110 volts AC. With the meter grounded to the 110 neutral side, white wire in the receptacle box. Touch each side of the fuse. If you see nothing it may not be a 110 fuse and you will check 12 volts next. If you see 110 on one side only the fuse is bad. Fuses can look good but still be bad.
If you saw nothing when testing for 110 the fuse may be on the 12 volt
supply. Set the meter for 12 volts DC. Ground one side of the meter to the trailer body and touch both pins that supply 12 to the freg. You should see 12 volts on one pin. This is just to test the ground you selected for the meter. Now touch each side of the fuse. If you only see 12 volts on one side of the fuse the fuse is bad.
One of these tests should answer any questions about the fuse.
As for connecting 110 directly to the heater element you can do this to test the element but keep in mind you will not have a thermostat in the circuit. If you go this route I would remove the element wire from the board and make the connections directly, 110 supply to the element.