I detailed a bit of my construction and flights on the forum
Baa Baa Black Sheep. There are some other approaches as well, but I just cut out hobby plywood to fit around the retract as a mount and then cut into the bottom of the wing to add additional foam support and the mount on top. I glued it in with hot glue, but my new mount I just put in is using foam tac. I screw in the retract to the mount and there we go.
The difficult issue is finding room for the wheel to fit in the wing. There is not a lot of room in the wing of the Master Series Corsair so I have had to mount the retract a bit lower then I would have liked. It just barely fits. I'll include photos and details on the new retracts in the Black Sheep forum when I finish the new install. Hope this helps.