Rockdoc, I've used regular Acraglas epoxy, West System, and numerous other brands. I usually use lacquer thinner and/or a heat gun when I wish to thin my epoxy. No more than 10% thinner, and don't overheat the epoxy to the point of smoking or you will really weaken it. Hot epoxy also sets up much faster, and you could lose your batch if it kicks over before you get it in place. I know that Brownell's simply repackages a good quality commercial epoxy, so there are places to get the good stuff much cheaper, and in larger quantities than buying those expensive little jars of Acraglas. One source I found for very good cycloaliphilic epoxies is Progressive Epoxy Polymers,Inc. Their website is
www.epoxyproducts.com The guy who runs it is a very good source of information on different types of epoxy, fillers, etc. You will learn a lot you didn't know if you navigate through the website. I'm also still using what's left of about 15 gallons of commercial epoxy and hardener that I bought at the liquidation auction of a local fiberglass boat builder about 20 years ago. I used several gallons to fiberglass a sailboat hull and many other projects and repairs. I have no idea what the shelf life is supposed to be, but it still seems perfectly good.
