I shouldn't have left that as a puzzle.

Open bay wings give you hatches all over the place. You just cut out the covering where you need a hatch. The new hatch cover comes off the roll of UltraKote the color of the cut out covering.

Guys do it all the time. I just put braces into an ARF. The elevator and rudder pushrods were not supported in their length. So I cut out the covering in one side where a lightening hole is, reached in and built a couple of braces, and recovered the hole with covering that matched. It's quick and easy.