I have slide try and it holds 2 batteries just fine even the siding under the compartment is totally roten.
I bought camper with some damage and the leaks completely deteriorated the plywood under the sides bottom and I peeled 2 layers of loose wood leaving last layer on for couple of seasons.
This year I come back and laminated whole thing with fiberglass, but there is a frame under the box that holds well regardless no siding.
The bolts after 10 years were in poor condition and all broke on removal.
I replaced them with stainless steel and fender washers.