For the holes, are they round or oddly shaped? If it's the latter, are you opposed to patching and sealing those holes, and drilling new ones? If you drill some new holes in a standard size, you can get nice neoprene or silicone cable glands to fit them. Those will seal around the cables without having to use a caulk or sealant.
x2 agree with Ductape ... my Magnum does get hot when it's doing heavy charging, or running the microwave / air conditioner ... might want active cooling for this storage bay, like fans on the vents. Noctua makes a great high pressure industrial fan, waterproof and everything. Get the 24 volt model and run it at 12 volt for low noise and long life.
