Will gasket material seal the rear bumper storage?

[tvanwave]

I'm in the middle of replacing a 3' x full width section of the floor in my 1991 limited. Pulled the inside panels off, cut the old bolts off, and now have unfettered access to the leaky bumper storage cover. I pulled it out, cleaned it off and now want to reseal to prevent leaks. I don't want to use vulkem because it will never come out again if need be. I was thinking of using a layer of waterproof gasket material above and below the plate so that when the floor is bolted down the gasket will be pressed into a tight seal. Has this been successful for others?