I just built this as my first DIY project. It was actually much easier than I was expecting. I'm not very mechanically-savvy, but I can follow directions... No leaks, drains perfectly.
I picked up a 10gal cooler at home depot. It has a big home depot logo on it instead of the usual rubbermaid one, but it was only $40 (I saw them elsewhere for $60-70). The parts were about $35, maybe $40. (When shipping is factored in, it was about as expensive as buying a kit from bargain fittings.)
I had difficulty finding the 5/8 SS fender washers -- actually I had difficulty finding 5/8 fender washers period. I did some substitution. I found 5/8 neoprene washers that are both waterproof and heat resistant. I used one on the inside in place of the SS washer. On the outside of the cooler, I used two neoprene fender washers with a 5/8 zinc cut washer in place of three fender washers. It isn't as steady as going all metal and twists a little in the rubber fitting on the inside when you turn it on and off, but there's no leaking after letting water sit for 30 min and not a drop when I turned it on and off.
Thanks a million to the OP and the clear directions and pictures on this!!