I think dowels and glue are poor choices for deck board material. With that said,Gorillo Glue or any other urathane product if you insist on glue. Logic being that moisture cures urathane and deck boards usually have high moisture content.

With modern glues a properly done long grain wood joint is stronger than the wood itself so things like dowels or biscuits are really unnecessary. The key is to have nice straight edges which typically means using a jointer although there are other methods using table saws or routers. Don't buy into any "gap filling" claims by adhesive manufacturers, do the joint properly.

Deck boards, especially pressure treated, have a pretty high moisture content which means the wood has a tendency to move as it dries, and move a lot. If you go that route, you would better off letting the wood dry for several months before starting you project.

I prefer Titebond III over the urethane glues just because it's easier to work with but urethanes work just fine for exterior applications too. You can also use rescorcinol or epoxy.

Thanks to those who replied to my request. Your opinions have been taken on board and appreciated.

Barry.