Bshin, I epoxied the belly pan where it sits on the wing. Make sure you peel the plastic covering first carefully. I also used some 1 inch long screws on both sides to anchor the belly pan to the cores, and epoxied the screws also into the cores. Drilled two holes for access to the wing mounting screws through the belly pan, so I can reach in with a socket head adapter on a screwdriver to turn the screws. The small holes do not seem to cause any problems. Make sure you do the permanent installation with the wing fully installed on the fuselage so that the belly pan is installed with correct alignment. My belly pan front lip seats very tightly on the fuselage and just behind the landing gear so there is no chance of any air knocking it off.

The lowermost part of the fin barely passes through the bottom slot for added strength. Are you sure you are seating the fin fully? It will only be flush with this lower slot, so when it does go thru the upper and lower slots, the fin will be locked from moving side to side. If it is a little too short, extend it using some scrap balsa glued under it to make sure it reaches the lower slot. I love this feature as it seems to give the fin a lot of extra strength.

Good luck!!