Re: Epoxy additive???
You really will not gain too much using the epoxy (or as much as you think). For adhesive between those two pieces you can use gorilla glue or even liquid nails and clamp the heck out of it. You can use screws as clamps but remove them after it has set up.
When you seal the wood and then you can use the west system epoxy and some fiberglass cloth on the outside.
West system is costly and no need to waste it without gaining much benefit from using it. I'm trying to save you a few bucks and leave the epoxy for where it is needed