What do you do in place of the gear doors?

The Construction Guide has you fit the gear to the retract rails, then remove it and plank the nacelle. I think it would be easier to leave the retract and the strut in the "up" position inside the nacelle, then finish the planking. Let the glue dry, sand everything smooth, admire your handiwork... and then do surgery on it (believe me, it took some guts to hack into the nacelle!)

Push the strut down until it contacts the inside of the planking, then carefully begin to cut a long, narrow hole in the planking and internal formers so the strut can swing down to the fully extended position. Then put the wheel on the strut, retract it until it hits the outside of the planking, and cut enough of the surface away so the wheel will retract fully into the nacelle. You'll probably want to extend the hole so there's 1/8-1/4" of clearance on all sides, and make all the sides nice and straight, with smooth radius bends on the ends. You can do the same for the nose gear once you've sheeted/planked the fuselage.

Then fiberglass the outside of the nacelle for strength. You might also want to fiberglass as much of the planking on the inside of the nacelle as you can comfortably reach. It adds strength, and not much weight.

Fred