The shore power converter provides 12vdc directly to the camper through the fuse panel.
The battery has an auto-resetting fuse, looks like a Lego block, with two posts on it. It could have a red plastic or rubber cover on it.
If those connections become high resistance due to corrosion, you will lose the connection to the battery.
There may be another similar fuse under the tounge or under the pin box to protect the tow vehicle from shorts. If so you must check there too.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW