Since the model will be on its gear, there needs to be some material removal and mods done.
First is to cut the bottom of the fuselage as shown. This will accommodate the landing gear bays.
and a quick look at the fuselage only
here are the frames and supports
reinforce the fuselage inside sides as they are too thin and will wrinkle otherwise
add rolled up card to support the wing spar
then glue the spar in place. It is now supported properly.
add the triangular support on to of the frame ( not the middle ). There will be a lower triangular sheet as well later on.
Additional cuts are needed in the spar to clear the landing gear bays.
Isaac