What if i doubled up the walls on the enclosure would that work as well to make a strong box? Or fiberglass the inside of the prefab box i bought?
I have used Line-X Bedliner spray to coat the inside of prefab boxes to keep from blowing them apart but you have to know someone who makes the "real" stuff and not the kind you buy in a can.
The problem with bracing most prefab boxes is you can't really install full width skeletonized braces without taking the baffle off so you end up putting in triangle braces or multi-piece braces and if not done correctly they can rattle loose. Some of the boxes that I've been asked to "fix" had so many holes in them from drywall screws that were used to try and salvage a blown out corner or securing an angle brace and missed that it was easier to take the box apart and glue a new piece of MDF on in place of the damaged panel.
Doubling up the walls is the best idea but you have to take off whatever they put on the outside (carpet, vinyl, paint, etc.) and sand it down to the MDF so you can glue the panels you add to the existing enclosure. Gluing the entire mating surface so they become laminated together is what creates the strength. But if you have the tools to make the panels for doubling then you can make your own enclosure and do the internal bracing correctly. You don't have to Dado every mating edge to make a strong joint (it does help because it makes more glue surface and stabilizes the joint so it is easier to make that joint straight) just realize that it takes multiple days to glue up one enclosure as you wait for the glue to cure before proceeding to the next panel.
