Wiskybuck,
When I first bought this shop 13 yrs ago the GTAW machine had a 5 gal bucket with a small volume fountain pump on it. But all the hose adapters/fittings were a nightmare. When it gave me even the slightest excuse I bought a Miller add on cooler and set it on the tank rack on the back of our Miller GTAW machine. The way my welder sits I couldn't put the Argon tank on the rack anyway, so the cooler sits there.
Personally, building one isn't worth the hassle. But the bucket with a fountain pump does work. Just takes some creative modifications.
Have a Great Day, Brent