On our '99 as you look in the battery bay high on the left side toward the frame you'll see a heavy red cable leading up to a small (~1.5x5" at a guess, dark and cold out there) fuse holder attached to the left bulkhead, the cover just pries off and you'll see a 300A fuse held down by 2 lugs.
The fuse was blown on ours when I went to pick it up. None of the outlets would work and the batteries were not being charged by the inverter, so if you have any function at all out of the inverter that's not the problem. Also the outlet behind the passenger's seat is not powered by the inverter on our coach, wish it was as that's were I sit when parked.
The above post is just my experience/opinion which is worth exactly what you paid for it.
'05 Lance 845/'06 F-250 or '99 Alpine 36SDS Usually towing an '01 Wrangler locked on 35"s or moderate '98 Cherokee on 33"s (rear locker only)