Crusty they are so easy. Basicly you frame up a bay between the ribs with some hardwood or ply, making sure it is resesed 1/16" below the wing surface. Then you make a 1/16" ply hatch to fit. Cut you arm hole and the epoxy two hardwood mounts on the hatch. Cover, and mount your servo and you are done..

The first photo is of a mount I retrieved from a bad crash. You can see the remainder of the ribs on either side of the hardwood rails.

The second is the outside view. You can see the 1/16" recesses of the rails. I cap the rails that run lengthwise with 1/16" balsa to complete a smooth frame.

The next shows the servo lugs. I use a little piece of a cracker box or like thickness between the servo and the lugs to make sure the servo has some wiggle room on the mounts.

Next is the hatch setting in the frame waiting for mounting screws.

The last is with a servo mounted.

I like the Dubro #2 sheet metal scrws, with the socket screw head. #254 if memory serves me right. They provide a low profile streamline head. Don't know if it helps with the aerodynamics but it looks goodl

Don