Just an update. I played around with my cooler again yesterday, tried different variations of washer/oring setups, but to no avail. Actually, my first try, I thought I had done it right. No leak from between the cooler body/outside washer........then it started leaking between the two outside washers. I figured, "okay, I got it this time. I'll take it apart, put more teflon tape on the nipple, assemble it like I last time, and we'll be set!" Nope. For some reason, I couldn't replicate how I did it the previous time and this time the leak was from the cooler body. Either way, there was still water getting into the cooler wall from teh inside.
Defeated, I cleaned up, went inside, and hopped on my computer to order some things from Bargain Fittings. Ended up getting the 1/2" NPT flat silicone gasket, a large red 1/2" NPT flat silicone gasket, and a 1/2" NPS flange locknut for the inside-cooler part. Hopefully I get it in soon and it works....this leak is taking time away from my christmas old ale.