We learned everything we know about belt in tube from 2791 but I will agree 100% that it is very robust and actually pretty simple once you get the hang of it... (And have machining capabilities)
2015- 1.5x3 side rails, 6" Colson wheels, 1/8" drop- 24 tooth pulley stock used to make custom pulleys that we counter bored to eliminate the need for a spacer on the bearing. Image below:
http://imgur.com/goFii7G
2016- 1.5x3 rails, 6" West Coast Pneumatic wheels, 1/8" drop, 24 tooth pulley with the counter bore.
The only negative I have with this set up is how much it weights, but the trade off of not having to touch it after we set it up is worth it to me.