I'm doing one now . . . This is a NON issue. The Transom on my Seafari is 2.5" thick!! and the outer fiberglass skin alone on the boat is almost 1/2" thick. Neverending you're over analyzing this bracket thing. We'll never come close to pushing the limits of these boats with the type of boating/fishing we do. If you are thristy for more answers get a copy of elements of boat strength by David Gerr.
800lbs is nothing. Even the ones that are hollow are incredibly strong. I'd say Hermco is right on with the less material remark.
And if your next concern is fasteners . . . well I lifted the entire stern of my 20ft wellcraft off 5 inches off the trailer trying remove the powerhead and free ONE frozen 10mm bolt on a yamaha 200hp. 20 bolts holding a bracket on the back of a boat will never come apart.
