Bumper Chain Box Lid Latch Ideas

[Wildergarten]

Hi,
I'm planning to put chain boxes in the front bumper on either side of my winch. They'll have diamond tread plate tops on hinges. I'm rattling around my head a scad of various ledges and latching systems. I don't necessarily need it to be lockable, although that would be cool. A badass magnet pulling them down against rubber sheet would keep them from hopping. I'm suspecting that sealing them perfectly enough to blow off a drain is borderline hopeless, but even mouse-proof drains big enough not to clog with leaves and such are a peril. I found some stainless hinges that will do, but even that wasn't easy.

The problem is that evey one of these possibilities is convoluted and demands precision, especially because of the curved end of the bumper (AKA "time"). I'm familiar with marine deck lids, and doing that right is a major pain. Has anybody done this and found something simple using easily obtainable parts? Or am I doomed to tedious iterations?

[Wildergarten]

This was the same bumper during fabrication on the previous truck.

[PwrWgnDrvr]

Harbor freight sells badass magnets in 150# and 250# pull. Inexpensive. Pull them out of the box and check them on the shelf. I found some that were defective with very little pull. I use them to keep tarps over the bed of the truck when its raining. Will even hold the tarp on while driving around town.