Sean,

Shrink your plate down to bolt on to the right and left of where you have the bolts now. Mortise this plate into the main plates attached to the spars. Then glue ply blocking underneath the "edges" of the plate where the retracts bolt in. This will give you some thickness at that perimeter. Then mortise in the thickness of the retract flanges. Then sand the main plate flush with the sheating. This way you can also have a bigger area of consistent glassing/paint up to the break away plate.