Weatherproofing access panels

[Rhino]

I'm currently working on finishing up my rear suspension (parallel 4 link) on a '68 Camaro and needing to decide what to do with my coilover crossmember. So far I have two routes I'm contemplating.

1.) Doing something similar to DSE and make it from boxed 1/8 plate.
2.) Make a tubular crossmember and cover the hole in the trunk with a fabricated sheetmetal closeout.

I'll have more adjustability options for ride height and have the added benefit of making the closeout removable for easy access.

My question is in regards to having a partially removable trunk floor. The car is getting built to be driven, and living in the midwest, it will likely see a moderate amount of rain. When that situation presents itself I'd like to keep the dry stuff dry, and the wet stuff down below.
Has anyone ever tackled such a situation? What did you use to secure the access panel? Have you been successful in keeping a weather tight seal? My first thought was dzus fasteners and some form of weatherstrip, but haven't used them in the past and don't know if the fasteners have that much flexibility in mounting depth.