I use braces (3/8" X 3/8") epoxied on the inside of the fuselage and then a thin (1/8") sheet of plywood above it. I cut some holes in the plywood for heat dissapation. I screw the plywood into the braces with small wood screws. Then I remove the screws, CA the holes and allow the CA to dry (this hardens the threads on the holes). I wrap the battery in foam and place it between the top or bottom of the fuselage and replace the plywood cover. Works great and I have easy access to the battery (simply remove the wood screws and the plywood cover).