I've alway thought that would be a good place for a battery or, air ride pump and tank. with a drain hole, you wouldn't be concerned if a little water got in.I'm sure i have read some other posts on this subject, we had the same idea. But in lifting the panel it's clearly a water trap, we had to cut & patch some rot. Your problem is as always, getting a good seal, let's see what reply's you get. It does appear to be a waste of good space.