Bob, Tom Yost is of course the ultimate expert, and I hesitate to tell you to ignore his instructions, but there are alternatives. For my very first build I coated the plywood with epoxy resin. It worked fine, but added a lot of weight. Afterwards I discovered that lots of people do other things-no coating at all, deck waterproofing mix, Danish oil, etc. For several boats I have used a homemade mixture of varnish, linseed oil, and mineral spirits. It soaks into the plywood, and after half an hour I wipe off any excess. I have never had any problems with plywood rotting or delaminating.

Some people use epoxy to glue the lashings, others do not. Each works, and each has its advantages. I would not consider using polyester resin for this. If you're going to do it, use a good epoxy. If you want to save money, don't do it at all. As long as you get the lashings nice and tight you'll be fine.

Epoxy does not adhere well to aluminum. There are some fancy industrial adhesives for aluminum that would probably work well for your inserts, such as Loctite H8600. But rivets would be the safest and most economical method.

Hope this helps.

Jeff