I have my ProS in a large Gitzo camera pack -- don't recall the bag model number, but it was about $300 from B&H (I'd never have spent that much, but I had a gift card for fifteen years at my current job and hadn't found anything on eBay that was big enough). I think it's
this one an they offer a larger one just in case you want to carry a spare body and 250 mm or 350 mm lens...
It holds the body with waist level finder and mounted 127 mm, plus 90 mm and 50 mm with mounted 0.45x filter, left hand grip, prism finder, three film backs, lens shade for the 90 mm and 127 mm, and in side pockets several spare or exposed film rolls, 70 mm filter set, other accessories, and a couple half liter water bottles in the top pouch (and room for a sandwich etc. if needed), plus I can hang my carbon fiber tripod on a loop from the side. I could pull one divider and replace the 90 mm or 50 mm and one film back with my 185 mm if I expect to want that The shoulder straps clip together and there's a waist band as well, so even though the full pack weighs over thirty pounds, it's not a significant strain to carry. It does take a minute or so to shuck it off and open it, then I still have to mount a film back and the left hand grip or tripod plate, potentially switch finders, etc. -- but for a camera like an RB67, that's a given anyway; this isn't a Leica or Contax you'd carry around your neck, ready to shoot (I've tried that -- even with just 90 mm and waist level finder, it's heavy and awkward for neck strap only. I'll stick with a folder if I want/need to shoot that way).