Battery compartment corrosion - Options?

There are probably various ways that a battery compartment, or at least holder, could be fabricated. Welding one up is certainly a reasonable possibility, but maybe it would be practical to do something like having a basic support framework to support the weight and attaching enclosing bits with screws or rivets or what have you.

It's probably not necessary to have it enclosed to any great degree, truth be told. It ought to be more or less sealed from the interior of the RV assuming you don't have AGM batteries, but otherwise it could be mostly open. On my class C just has a tray of sorts assembled from a few pieces of angle iron welded together. I modified it somewhat to add a bit of height clearance and permit GC2 batteries to fit by bolting on different angle iron bits. (A more enclosed tray would help keep the batteries and connections cleaner, of course.)