I'm coating the whole thing in "HEMA knutsellijm" (= cheap-ass hobbyglue), works really nice!
Its deludable in water, so i can just paint on a thin layer, and when it dries (takes a while) it leaves a completely invisible, waterproof skin. its strong but still flexible, and it allows the surface to be sanded REALLY smoothly..! Also it doesn't have that yellowish look to it, like woodglue or even uhu-por tends to have after some time.. I coated the servo compartments inside the wing extra thick, and there it shows an almost green/blue pearly quality.. and after sanding.. it just feels smooth as silk..!
these are things I can not show you on internet pictures, but I'm lovin it!