I sprayed my cavities with rockerguard, then made a nice padded bag for each side and then use them for my emergency kit - all the stuff you need in an emergency - zap straps, some tools like wrenches, pliers electrical tester, screw driver, emergency blanket, different types of wire - electrical tape, tire plugs, road flare, fuses etc. look up what to take on a rally and basically thats what I put in there. I think there is even a couple tiny bottles of Buffalo Trace Bourbon, couple hot wheels for cranky kids and a couple knives (filletting and a chef's knife and a sharpener) there is nothing worse than showing ap at a bbq and the hosts knives are so dull they don't cut.
If you leave your car out in the rain this area will fill up with water so I didn't glue any foam in there.
Both of my cavities were rusted out and the previous owner just filled the bottom up with chicken wire, newspaper and bondo. I removed that and made new bottoms out of galvanized metal and welded them in.
