Hey blu, it's been a while.
Had the same issue with cutting a hole in the panel and I really didn't like the look. I made the cover out of a piece of 20 gauge then riveted it on but panel adhesive or seam sealer would work better. Didn't have any. I plan on covering the panel in some thing as part of the trunk finish whatever that turns out to be.
Spent the whole day underneath and inside the trunk sealing and riveting 5 of the six panels permanently into the car. Feels like progress.