Can anyone provide a good reference for Master Trust filing instructions?

I use RIA's Employee Benefits Compliance Coordinator (a print loose-leaf services), PPC's 5500 Deskbook (also print), and RIA's Checkpoint (http://www.RIAcheckpoint.com), which incorporates both of the print products. You can get any of the three Pension & Benefits libraries through Checkpoint; all three include both publications. (Pension & Benefits Essentials, or Pension & Benefits Advisor, or Pension & Benefits Expert).