12v 20A circuit keeps blowing blade fuse

[rayandre]

So we got back from a month long trip out west dry camping in national parks for about 3 weeks. I'll preface this by saying I replaced the converter, fuse block, ground and installed a battery disconnect just before we took off for and headed west back on July 5th.
We had (almost) no issues until we got to a state park on the way home, plugged in using shore power, and popped a fuse at some point. The circuit has our bedroom wall lights, a center light in the ceiling by the kitchen and our front ceiling fan on it. I replaced the blade fuse (20amp) and tested it on battery power only and it worked, then plugged in and blew it again. I didn't worry about and we drove another 450 miles one day and tried the whole thing again at another SP-same results so I left it alone. Any thoughts on what could cause the shore power to pop a fuse on a 12v panel?

[65CV]

Possible crossed wires after all that driving? Not sure how well '70s insulation holds up.
If you have a multimeter, you can test each leg to be sure there is no 110 on the circuit.