The hull is not heavy at all if you remove all the nitro motor "bs" fiberglass engine mounting "mountain" and the heavy fiberglass radio box. In fact, it will weigh in at 1 lb 12.9 ozs. once that is done and the paint is sanded off. I'm in the middle of a build myself using a Fieago 12XL from Offshore Electrics and 2 3s Lipos. I am using the oem Aeromarine nitro hardware for now becuase it is actualy very nice stuff.

Strip eveything out of the hull and p/u some 1/16 plywood from your local LHS and floor each of the sponsons for battery trays. Vac-U-Boat makes a real nice wood/aluminum 80 degree motor mount that will fit the bill perfectly, although I am making my own.

As for batteries, I would suggest 16-18 NiMh cells or 6s Lipo for voltage.