The oval inspection panels are not removable, for inspection purposes this would be better.
The oval inspection panels are only for bolting the fuel tank to the main spar, thereafter they are riveted with 3.2 mm rivets to the skin and painted.
To inspect the interior of the wing during an annual condition inspection one can only use the 2 larger / square inspection panels.
These 2 don’t give you access to the entire wing interior and removing the rivets every year is not practical.
I tried M3 rivnuts but there is not enough edge distance to increase the hole and the collar of the rivnuts prevent the lid to be flush with the skin.
I designed doublers from Aluminum 6061-T6 (thickness 0.032 inch) and let them fabricate by Big Blue Saw. The edges are a bit rough and the 3.2 mm hole came out a bit larger, anyhow I’m happy with the result: