Double Barrel Smoker

The short answer is yes... will be necessary for the required draft and heat.
Found that out the hard way.

Barrel burn-out
http://www.bbq-brethren.com/forum/showthread.php?t=41855

Initial build
http://www.bbq-brethren.com/forum/showthread.php?t=45656

Grease drain mod
http://www.bbq-brethren.com/forum/showthread.php?t=46215

I only have a single on mine. I have no problem with draft at all, but it is hotter on one end. A double tube setup would remedy that.
The biggest thing to remember, is that they are fuel HOGS!! plan on using wood, and do a bunch of tests to figure yours out.
I absolutely love mine, but if I made another one it would have 2 tubes connecting the barrels.

I put 2, 6" pipes from the bottom to the top, both have dampers in them, and 1, 6" stack out of the top, which also has a damper. I've not had any problems with hot or cold spots. I also bought [2] Vogelzang kits, so that I could put a fire door on either side of the burn barrel, this way no matter which way the wind is blowing I can open the door to catch some extra draft and get it up to temp. quicker.