Bolted the center wing in place last night and glued on the rear fuselage turtledeck. With the wing off it's very easy to get access to the insides back there for the turret work, so not worried about permanently mounting this piece now.
Here's the part where I need some help coming up with ideas though.
The wing is held on by 6 nylon 1/4-20 machine screws. Since I couldn't find 4" long ones anywhere, I went with ones that are 2" long which means the tops are recessed down into the wing. Since the wing is hollow anyway, this worked out OK up to this point. I cut a hole down through the top of the wing and glued in some spacers made from dowels to keep the screw lined up with the nut in the fuselage and not flopping all over the place.
Now the problem - the holes left in the top of the wing are fugly, and I'm not sure how I want to deal with them. I'm sort of leaning towards fiberglassing over the top and then drilling a hole just big enough to put the screwdriver through so I can operate the screws. This will give a better looking top surface, keep the screws from falling out and getting lost in transit, but if I break a screw on landing/crashing I'll need to cut the hole bigger to replace the screw. Chances are if I hit hard enough to break a screw I've got plenty of other work to do anyway.
Another idea I'm not sure how to "operationalize" is making plugs of some sort. Just not sure how to hold them in - magnets would work if I switched to metal screws instead of nylon, but then I lose the advantages of a planned failure point.