Nice photos, nice jig!
If all 3 corners are made strong, there shouldn't be any problems with the framework twisting. I use more like 3/16"-1/4" thick ribs, plus I like to use 1/32" ply rib doublers in the engine bay.
Control of these planes can be real smooth and precise if you use the inner servo arm hole and pivot the flaps about 1 1/8" up on a tall control horn.