BMatthews

I would stick with the scale airfoil thicknesses on the horizontal and vertical tails. The horizontal will likely come out quite thin and that's fine. For the vertical you WANT the thickness from a purely structural standpoint. With the stabilizer being mounted so high on the fin there's a real need for structural strength in the fin. You're going to want to treat this part of the design as if it was a load bearing wing with suitable structure and a definete tie in to the fuselage. A couple of plywood fuselage formers that have vertical stubs that extend up into the fin to tie into the fin spars would be appropriate. You want to keep things light back there but not at the expense of structural strength. Ribs, spars and a structural skin such as 1/64 or maybe 1/32 ply for the lower section of the fin up to the stabilizer mount would not be misplaced. Or if you make it from foam then the stubs should extend up into the foam and be formed so they are at the outer surface so the plywood or balsa skin can bond to them. For a foam fin 1/16 ply for the portion at least up to the stabilizer would be ideal. Light but far stronger than a balsa skin at carrying any side loads you'll encounter during flight or less than perfect landings.

12% seems pretty thick from the looks of the pictures I'm finding. I can't seem to find any good drawings of the Mig so I can't measure anything. But by eye it LOOKS like it's down around 7 to 9% thick.