I suspect you have your battery installed in REVERSE POLARITY. Observe on the side of the 12VDC battery case and find the word "NEG" or the symbol "-" and grab that connected battery cable and make sure this cable goes directly to the trailer FRAME GROUND connection.
If that fuse was blown your two REVERSE PPOLARITY fuses onyou 12VDC Power Distribution Panel is most likely blown as well...
I did say SUSPECT. It could be just like the others have said bad connections around the fuse.
As big as those fuses are it sure takes a heavy load to blow them...
just my thoughts
Roy Ken