I did exactly the same mount on an old Goldberg Chipmunk whose gear ripped out of the wing. Re-enforce the fuselage bottom with another layer of plywood (at least ¼-inch) and glue it in with triangle stock up the sides of the fuselage.

I would also suggest you go with nylon bolts (http://www3.towerhobbies.com/cgi-bin...?&I=LXK194&P=7). With #10-size, I would mount the gear with 3 bolts. That way, the gear will “break away” with a rough landing instead of ripping the bottom out of the fuselage.

This setup “worked as advertised” when I was horsing around and overshot the Chipmunk into the rough field beside our runway…[X(]

Edited: I forgot that I drilled and tapped right through the fuselage bottom (lite ply) and into the 1/4-inch hard plywood. Then hardened the threads with thin CA and ran the tap through again after it dries. If you break off the nylon screws, they are easy to drill out using a screw removal tool or if you can grab the other end, just thread them back...