Sorry, don't have time to read through the posts to see what was suggested. So if I am suggesting the same as others, my apologies....
The WFCO panel (if it's the one I am thinking of) should have 2 40a main fuses to protect it from power surges or reverse polarity. If the converter is stand alone it will have it's own fuses. There will also be a fuse at the batteries, or a self resetting 30a breaker which may not be visible which could be the fault. My last trailer had 2 of them hidden under the trailer. I had to remove an access panel under the trailer (which didn't look like an access panel) to gain access to them.