Honestly, after reviewing the numerous thread additions, there are really great points to consider here. However, I'd offer potentially, a simpler solution to the many well made points, specifically when it comes to cost compensation to the project.
I was really concerned with this subject and mutually digressed into costs to replace such a small transom, even on MY tiny 14' Sea Nymph, though, I wanted it to last for the remainder of its life. I decided to go with REGULAR 3/4" plywood, but apply at least 3-4 coats of fiberglass resin and sanding in between. Note; I live in Tucson, AZ so I accomplished this with dry and very hot conditions and over a two week period giving into extremely quality drying sessions in between. That being said, I have a rock hard application that no doubt, nearly a year later has shown zero deficiencies what so ever. I consistently change out my motors on the transom and it has yet to damage/pierce the epoxy base much less even being concerned about the wood becoming infiltrated. So, the answer to MY questions was answered using leftover 3/4" plywood, non marine grade and less than $40.00 of epoxy resin. Being an amateur, I believe I got the best bang for my buck in my application against cost and for the size of my watercraft. Sometimes we overthink things and Transoms are one component we want done correctly but I do believe this was a success on a nearly half-century old chasis and will likely outlive the rest of it.
