In the mid '80's (at the age of fifteen) I built a Norm Page Mach One from plans. I cut my own foam cores for it. Being young and immature I wanted all the cool stuff from that era on a plane that wasn't designed for it, so I modified it with a half-enclosed tuned pipe along the top of the fuse.

Not having anyone around who could advise me on painted finishes and foam wing sheeting, I made two big mistakes which led to my model being grossly overweight: My prep for the paint on the fuse was grossly overweight (don't ask), and I used the wrong glue to sheet the wings (ditto). I think the all-up was close to 5 kilos (eleven pounds) which included about a quarter kilo (half a pound) of lead in the nose to get the CG back where it was supposed to be!!!

But I did get one thing right which could be useful background info for your build. My wing root joint and main retract mounts were massively strong. And I too had two servos in the wing root - for flaps and ailerons using a concentric torquerod setup a la Hanno Prettner's Curare of 1977. I simply made a rectangular servo cutout in the wing root big enough to take both servos side by side.

The strength was proved conclusively when the Mach One pancaked in on approach and met its demise (thanks to the added weight no doubt). The nose gear collapsed, the main gear wire legs were bent back almost flush to the wings, the fuselage split right behind the wing where the ply doublers ended, but the wings and main gear mounts emerged completely unscathed.

So heer's my two cents' worth about how I joined my wings and mounted my retracts.

My retract mount plates were just a bit bigger than yours, recessed into the foam, glued in with 30 minute epoxy and faired with balsa block. No rails, but I did make sure I had a good fit over the whole area of the joint. I reasoned, correctly as it turned out, that an impact on the retract leg would likely crack the whole wing or fuselage before it could tear a retract mount out of five or so square inches of epoxy joint.

I also did not glass the wing root joint because I didn't want the edge of the glass showing under my Monokote (Solarfilm actually - the British version), and also worried about the adhesion of the covering to the glass. Instead, I cut a spanwise slot in the top of the already sheeted and joined cores for a 3mm (1/8in) thick plywood spar extending to just 200mm (8in) into each wing. Spar depth tapered from about 25mm (1in) deep at the root to about 8mm (1/3in) at the ends. I inserted the spar from the top and glued it with 30min epoxy so that its edge was about 2mm (1/16in) below the wing sheeting, and built it up to the surface with balsa which I could sand flush with the wing sheet for a perfect surface. Again, I reasoned that any impact strong enough to either tear the spar out of about ten square inches of epoxy joint (in shear) on each side, or split the spar, would likely destroy the airframe anyway. My servo cutout was about an inch behind this spar as far as I recall, and it didn't seem to have affected the wing's capacity to absorb such a terrific impact.

Hope that was of some use so you can get back to making your servo cutout and stop worrying...

Best regards.