Tee sez
"My husband is rebuilding the seats for our bayliner. He has made the seat
boxes and is ready for fiberglass. He has sealed the plywood with resin.
Now is where we differ in opinion. I say that glass needs to be laid
anywhere that two points of plywood come in contact, i.e. the corners meeting
and the top meeting the sides. I even thought that fiberglass tape could be
used in the hard to get areas. He says that just applying the
resin will seal these areas.
....etc"

The resin may in fact seal the surface of the wood, but won't really lend any
strength at the joints. Fiberglass cloth is cheap compared to the cost of
"good" plywood and resin. What mechanical fasteners are holding the seat
"boxes" together? I'd wrap the boxes in a layer of cloth, with the fiberglass
tape you mensioned (GOOD IDEA!) added to reinforce the corners. Bear in mind
that ANY holes you drill in the finished structure must be sealed to prevent
water intrusion....water can seep in and not be able to drain/evaporate out
which will cause rot in time to come. That thought applies to whatever method
you use to attach seats to the deck. Trapped water is bad!
You are working hard on this, so don't cut corners!
Best wishes
Mike