subject

Two suggestions

One: Stay away from pour foam. Particularly if it may get exposed to
moisture.
Use Styrofoam blocks or factory cast polyurethane foam blocks.
Do not let anyone BS you. Pour foam will absorb water.

Two: For your transom. http://www.coosacomposites.com/
This is a very strong product that can be bonded between two sheets
of relatively
thin aluminum. I would bond with 3M 5200 or a like product. Bostik
920 would be
much cheaper and work just as well. I am sure some in this group
would insist on epoxy.

Good luck.