According to the instructions, the Rotochoks are the first things on, when pulling in and the last things off when pulling out. THat way, the unit is locked in place right away and can't go anywhere until you actually pull out.
By my observation, the add a huge amount to the stability of the rig when parked. I assume the other wheel locks like the X-chocks do the same, something that the ground chocks don't do.
2007 Chevy 2500HD Classic LBZ Duramax/Allison (Stock)
2005 Bigfoot 1500C8.2 AWESOME