I expect it will fairly heavy as I intend to use a 4 stroke and wouldn't the fuse/wings etc. require waterproofing?
No special waterproofing required inside, just take pains to be sure nothing can get through the covering. Nyrods, steel pushrods in a tube or even just pushrod exit covers work well enough to prevent water from entering there. Use foam wing saddle tape on all four sides of the wing to fuselage joint. Basically, if the airplane is fuel proof, it is waterproof.
Jim