Epoxy the tri stock to the firewall and fuselage sides. The stock firewall is butt glued to the sides with hot glue.

For the fuselage, look where the main wing goes into the fuselage. You will see how the sides of the fuselage are cut out for the wing. On a "not so perfect" landing this area tends to crack. On the inside, cut some 1/16" ply to fit the area and laminate in place with a THIN coat of epoxy - clamp as needed until dry, OR cut and fit some 3/32" balsa and laminate in with CA.

These are the two best known problem areas for the U-Can-Do