Some 1/8" hard-ply parts were made up to act as rails for the servo hatches to be screwed to, and epoxied inside the skin. There isn't a whole lot of structure keeping the upper & lower wing skins apart, so I intend to make up some balsa spacers to glue between the skins in the area of the servo hatches. That way, when I press down slightly with a screwdriver on the hatch screws, I'm not distorting the whole skin.

BTW, I've found over the years that when I cut the slot in a servo hatch, I often get it wrong - typically making a wider or longer slot in the hatch than is necessary. To deal with those mistakes, I now always use a simple balsa hatch substitute initially, and throw these away and make new ones as necessary until I get hte hole correct for the desired travel. Once that's done, I use the balsa cover as a template to cut the slot in the [i]real[i] hatch.

Here are all 3 hatches now completed.