I picked up a Dillon cover yesterday from Grafs for my 550B. Overall I'm happy with it and think it will get the job done (mostly). I especially like the fact that it is designed to enclose the ram and linkage. It looks really nice too! The one downside is it doesn't cover the accessories I have installed. This includes the bullet tray, loaded cartridge bin, and cartridge case bin. I also have the tool holder mounted to the back of my press, and while it is snug, it did fit around it. My reloading room doubles as a wood working shop, dog kennel, and general fix it shop, so it can be dusty at times. Looks like I'll be employing the trash bag cover when the wood chips fly or I'll have to keep the bullet tray empty and store the bins as well.
Brian