Irwin 28.5". No room to work to install backing plate in transom. Was thinking of putting backing plate on outside of transom in cockpit then fill 3 1/2" cavity in the transom with Evercoat 100654 Sealant Foam. I am thinking the foam would spread the push of the outboard over a larger area of the transom. The backing plate in the cockpit would just be acting to allow access to nuts and washers. Any ideas on why or why not this would or would not work?