I take every arf I build, stand it on the firewall, and flow gorilla glue/elmers ultimate, into every nook and cranny around the firewall and fuselage joints, let it swell up for a few hours, ties it all together really well.. Not one firewall torn out yet ...including a recent incident with my stearman where I broke both metal motor mounts ...rubber isolated dubro mount let go, instead of firewall.