I have tried the copper/brass drop leg racks.... made a large one that was cooled with water and air... it worked OK but with the price of copper sky high I wouldn't do it again. It also didn't remove all of the moisture. it just collected it and then I had to remove it manually from the system.
I can't stress enough that you need to really know what you're doing If you want to make one of these. Pressure vessels are nothing to fool around with, and welded improperly can kill you. (while welding and after pressurizing).
I drained tank, removed valve, set upside down for five minutes or so.. dumped some comet and dawn soap in the tank and pressure washed it out a few times. Took a big weed burner and heated the tank to burn off any excess. and went to hole sawing the holes in it.
I put a "Tee" right after my regulator on my argon bottle and ran a hose to the propane tank to back purge it while welding. Used painters tape to seal it up. Black iron fitting weld (OK) but if I had it to do over again I would use a little better grade steel.
tank has seen 135psi many times. full and empty of desiccant. So far, I'm still alive.