I first located the fuse ribs in the tail of the plane and then cut out the wall on one side of the plane careful not to cut one of the ribs then i used something like 3/16 balsa to build a floor, front and back wall this gave back the strength of the fuse after cutting out the wall, also provided support for the battery to sit and keep it in its place, then i cut and covered a new hatch to fit the hole i made.