Thank you very much, gents, for checking my clumsy work. I really appreciate.
For reference, here are drawings of the undercarriage bay I used.
Front undercarriage bay
Rear fuselage
Rear landing gear
Undercarriage bay 2nd rib
Undercarriage bay 4th rib
Undercarriage bay 8th rib
Undercarriage bay 9-10th rib
Undercarriage bay 9th rib
Undercarriage bay 10-11th rib
Undercarriage bay 11-12th rib
Undercarriage bay 12-13th rib
Undercarriage bay 13th rib