The last few pattern models I have done I've installed a removable battery tray. I make it out of a good grade of 1/8" 5-ply plywood. The cross pieces are 1/4" carbon fiber tubes. The mounting pieces are 3/8" plywood, with the front hold-downs 1/8" ply. I saw this system on another plane and I really liked it. If you have to do work on the model it's nice to be able to remove the tray. Plus If I need to change the position for CG I can make up another tray. And it's pretty simple to make.
Once it's in place I use the Hysol on the 3/8" mounts to permanently attach them to the fuse.