STEVEN:
I reinforced the firewall by taking two pieces of 1/4 in light aircraft ply laminating them together, Then copying the original firewall shape. Upon installing the new firewall I moved it back 1/2 in because of my TAURUS 3.2 motor mount I now can use my TRUE TURN spinner without the plane looking like BOZO the clown. Anyway I then pinned the firewall with !/8 in dowels. four on each side. Added triangle stock HARD WOOD of course, one piece each side. No fiberglass Not needed IMO. Very strong firewall no way I'll pull that loose. I've made at least 6 flights on the new set up and not a hint of looseness. All servos are mounted per instructions. Rudder mid plane, elevator's rear. No problem with balance, Right on the wing tube. No added weight anywhere. Which kinda confuses me. You would think by moving the firewall back 1/2 in I would have played with the C.G. But nothing seemed to have changed???. Actually I think the plane flies better since the repair. The only thing I can think of, Is maybe the firewall had been FLEXING with torque! I now use much less rudder on vertical up!! Who knows (not me). Anyway doing the firewall is no big deal I was surprised how quick it went. Just take your time It's a very easy but necessary repair. As for the on board started try to mount it under the wing tube along side the gas tank. I 'am sure you'll have plenty of room.
AJT ;^)