I would bet on a faulty coupler. I have had this trouble before. I bought a Milton air coupler and fitting and no more leaks. Whenever I buy an air tool, I make sure it has a Milton air fitting. Yeah, they cost a little more, but they are well worth the couple of bucks.
Yeah, you don't want a double vapor barrier. You could always tape up any holes that occur in insulation paper before you drywall. The facing paper on insulation isn't that great of a vapor barrier anyhow.
I buy alot of tools at fleamarkets, garage sales, etc. Where do most of you buy your tools? Flea markets? Brick and mortar stores? Online? Just curious as to where you acquire all the cool tools that live in your garage.
Looks good! I used an old tractor rim at my parents' farm for a fire ring. The heavy steel of rim won't burn through in a year like the metal of the fire rings they sell in the stores.