in need of a cooler

David, each coil is 20" long and how wide?

Stainless steel is used because of its energy transfer qualities in addition to its food grade properties.  Copper can not be used because finished beer is too acidic.  If you use copper, you can potentialy cause copper poisoning.  Copper is okay for water...but not for beer.  I've read around about using tubing on forums.  People have tried very thin walled tubing.  The overall consensus is that tubing does not cool the beer under operating parameters.  (ie serving beer where you are pulling draft after draft).  The tubing for ice machines will not work because of pressure issues.  The smaller the diameter the more resistance is required.  This translates into higher pressures from your regulator. You can use a formula to determine this:

P = L * R + H ÷ 2

P = Pressure in the keg in PSI
L = Line Run in feet
R = Resistance of the line per foot
H = Height from the middle of the keg to the tap/faucet in feet

in the small diameter ice machine tubing scenario...you need a lot of it to allow more than 12 ounces to sit in the line...even then the heater transfer has been reported as not that great.  I have no idea what the resistance of the tubing is...but here is an example using 3/16" hose (standard size beer line with a resistance of 2; ice machine tubing is much much higher resistance when comparing diameter size)

P = L * R + H ÷ 2  .......if we plug in a resistance of 2 and height....lets say 2 ft. between keg and tap, and 50 ft of tubing (I would think that you would need more than 50 though to get beer cold quick enough).  This gives us a required operating pressure of 100 PSI.....more than most regulators can handle and dangerously close to the max operating pressure for a corny keg.

P = 50 * 2 + 2 / 2

P=100

I'm certain David has researched/explored designs for jockey boxes. There's probably a reason he/they call for metal coils instead of plastic.

If we do a second jockey box for whatever reason, perhaps we can experiment with materials then....

that might work...

each coil is 10 inches wide....and there are two...so 20 inch or more will do.