Same as reviewer "Dean", I also chose to separate GearTrack channel at approx. 19".  Aside from being able to hang goodies below it, I chose to stack another GearBox below it -- you can't do that with 18" spacing.  I realize this means other pre-assembled/welded GearBoxes that have two GearTrack mounts wouldn't fit right...
Construction is great - I bought 4 and none had defects.  I like the way the hardware kit has a spare of every screw, nut and washer!
The one thing I'd recommend during assembly is to take your time to assure that EVERY sliding interlock tab is engaged properly with neighboring panels.