Ok, after some experimenting I've found what works for me. I decided to use 3/8" two piece shaft collars I picked up from grainger (10 dollars each). I found that one of these on each side of the frame below the top bar will fix the canted top bar issue by themselves. For that to work it took some fiddling with weighting the rack and adjusting the collars until they allowed very little movement of the top bar, as well as kept it level with the rack. I ordered a full set of bms tubular bars, including the heavy grooved bar, so I gave these a try without adding spacers and they worked fairly well, the grooved bar does the job of keeping the rope well centered, even though using a tubular slant bar on the top results in it being canted just like the u-bar. One thing made me uncomfortable with the bms tubular slant bar on top, when weighted, not only would it cant, but the slot would be pulled away from the frame of the rack. That way the only part of the slot in contact with the frame was the very edge. Technically this should be fine since the weighted rope would keep it from popping off, but if there were some bouncing or the like, I could see it being a problem. I tried using the spacers to cure this on the tubular bar, but couldn't get it to cooperate. Also, one gripe I have about the heavy grooved bar, the straight slot allows the the bar to fall away without resistance. I'm sure this is a safety feature to help prevent rigging backwards, but it's a real pita when packing/carrying the rack. It won't stay in place and gets caught on everything! It doesn't hurt a thing really, just annoys the crap out of me. lol
https://picasaweb.google.com/1157064741 ... directlinkI took the nice camera up the rope to demonstrate my new setup :)
So now I'm setup with a u-bar on top, spacers, bms heavy grooved 2nd, and bms tubular slants on down. I'm very pleased with how it operates, thanks a bunch for all the advice everyone!
A couple of side notes on the spacers:
Use two part 3/8" shaft collars, the solid and split are impossible to get around the top of the rack
Not really an issue for cavers, but adding spacers prevents the option of riding a double line (there's not enough room for two ropes on the rack)