What are the differences between the Standard, Roto, Ultimate Strength and other SKB racks? I recently purchased the XRack3, which is a Roto type. It is a 10.5" depth, with a front lid and rear access cover. It accommodates a Crest ProLite 2.0 amp and Sansamp RPM. I have to unplug the interconnects to put the cover in place. The rear cover makes for very tight access. I'm unclear on the differences between the Standard and Roto series racks. Both appear to have front and rear lids, and the Roto Ultimates have rear rails. Q: would those in the know, please post their lessons learned?