Been using a 6U and 4U gators for the last three years without a problem. I switched from a 4U Anvil mainly because of weight but I was also expanding my rig so it was convenient.
If you're going to be using multiple racks, mount the connectors you need on a stamped plate in the back of each rack and label everything. You want the labels to be clear enough so anyone could theoretically setup your rig. (this is mainly because sometimes I am rushing to setup and its nice when anyone can help, then its a quick glance to see if its done right)
I leave the back of the 6U mostly open, just in case I ever want to change something to suit a gig. But there is a 2U punched plate in back that I have all my connectors on (2 post outs for other power amps, a DI out, 2 speakons, 1 powercon, 1 input, and several outputs from different stages through my signal chain (in case the sound guy wants something particular or if I'm running stereo to a satellite rig).
I have all my preamp rack stuff and one power amp in the 6U and I have two other power amps each in their own 4U's. I use a prepunched 1U rack plate and a 3U perforated on the back of those 'satellite' racks and just 1 one of the 2U perforated plates on the front. Then I mount all the neutriks I need on those punched plates (power and signal).
2U Perforated plate:
http://www.parts-express.com/pe/show...number=262-102
3U perforated plate:
http://www.parts-express.com/pe/show...number=262-104
1U Prepunched plate:
http://www.parts-express.com/pe/show...number=262-575
Neutrik power-in (1 per):
http://www.parts-express.com/pe/show...number=092-284 http://www.parts-express.com/pe/show...number=092-280
Neutrik speaker-outs (2 per):
http://www.parts-express.com/pe/show...number=092-059
Neutrik XLR-1/4" (2 per):
http://www.parts-express.com/pe/show...number=092-042
I will say that because the gators are plastic, you should try to cover as much open rack space with blacks or perforated plates. It greatly increases the racks stability when stacking them and definitely makes them feel more 'sturdy'.
Also the lids are deep enough that if you want to on the back lid, rig up a cable holder. I just used two pieces of bent aluminum stock and a few pop-rivets to make a place to wind up the power and signal cables on my 4U's.
Having it setup like this allows me to take 'only what I need to survive' without having to un-rack anything or schlep unused gear in/out.