Well, might as well answer anyway. I would carefully block sand the old paint as close to the wood as you can get. using a block will be most effective. Take it right up to the fuselage. Then get some SIG Stix-It, or Balsa -Rite and give the last inch towards the fuselage a good coat of it, and fine sand that also just to remove any bumps. recoat if necessary. Then apply your wing covering and get the edge to within 1/8" of the fuselage. If you plan to repaint the fuselage, now is the time to apply the fillets, and have them overlap the covering to seal that edge down against fuel creeping underneath it. About 1/8" to 3/16" will do, or whatever looks right to you. When painting the model, you can mask off the wing covering along the bottom of the fillet. I make fillet material from finish cure epoxy and micro balloons and you can search out that method and the Super-Fil product also here on the forum. If not that concerned with looks, run the covering right up to the fuselage and then run a small epoxy fillet along the edge and let that overlap the edge. The key here is having something overlap the edge of the wing covering. Sometimes I just use silicone caulk as a fillet if strength at the wing/fuselage joint is sufficient. It holds up well to fuel and exhaust goo. It even comes in different colors now also.
Type at you later,
Dan McEntee