rear bumper storage area water issues

[goransons]

I have the beginnings of severe rust to the galvanized box that holds the black water tank on our 69. The angle iron is getting replaced, but it seems to me this area is going to continue to be prone to water collecting.

Has anyone else experienced this problem? I've considered drilling some small holes to let water out, but am concerned about them clogging up or otherwise getting blocked. I can't imagine the lid was ever water tight.

I do know there is solid sheet metal about 3 inches in, so I'm going to patch the sheet metal box for now and replace the supports. Eventually I want to reconfigure tanks but that's not in the budget for now. My concern is making sure that I minimize any chance of the problem again in the future.