our beds rot from the inside-out, so whatever you can see will be 100 times worse on the other side of the sheetmetal.
2door XJ rear wheelwells can be made to work, but they are close, not exact. plenty of owners have covered them up with bushwackers, but because it is worse inside the rust will always come back unless you deal directly with the rust behind it.
Getting access is the hardest part, but protects like POR-15 can help stave off the cancer attack if you can get in there to prep and treat.