There are a couple of good ways to strengthen the firewall. The first one is to epoxy tri-stock into the corners where the firewall meets the sides of the fuselage. The second way is to drill holes through the fuselage sides into the firewall, then epoxy wooden dowel "pins" into these holes. Then shave off the dowel and sand it flush with the sides of the fuselage. Both of these will give you a lot of added strength.

Ken