I just walked out an took at look at my 83
Burro. I've got the interior stripped while I do some gelcoat work. So I can see the structure. The
Burro has a gap between the inner and outer shells. Since they drove the spare tire mount bolts through both shells, one side was either tightened too much, or the
weight of the spare tire brought the two shells together on the Burro you're looking at. My Burro has a spare tire too, and a block of wood was put between the two shells at the seam to maintain the spacing. It's a pretty easy solution to your problem. I'd remove the spare tire mount, cut a piece of wood that you can put in between the shells,
fiberglass that piece of wood, then install the wood between the two shells and re-install the spare tire mount. I think that once you remove the spare tire mount and see what's there, you'll see that it's an easy job.