SlugLife
Contributor
If you are adding something new, you might consider adding L-Track or E-Track around the front and sides. Lots of options with those systems, including 2x?s cross-beams for cargo stops or cargo shelves/tables with the E-Track.
Those would work very well, just need to see if I can stand up the 40's
L-Track and E-Track are pretty awesome. I wish they were more common (they're most seen in cargo-vans and enclosed trailers). I've started using E-Track "everywhere" lately. (I'm even thinking about putting some in my sports-car trunk which would be kinda hilarious, but useful).
E Track Rail
Wood Beam Brackets
The advantage of ?-track is it's very configurable. For example, if you attached some kind of tank-holders to one of those brackets, you could remove it in seconds, and put something else on the track.
The track/rails and brackets linked should stand up to just about anything you can throw at them. They're used to tie-down vehicles and heavy loads. The question is really around whatever you build, or how they're mounted/screwed in to your vehicle.