IceCube
Registered
Just shell out for the DR SMP single tank adaptor. It adds a couple pounds of weight that you're going to need with the heavy wetsuit/dry suit for cold quarry diving anyway, not to mention the stability of the tank on your back. I tried to do it without the SMP and I hated the way the tank shifts on my back.
Recently bought a BP/W and tested it this weekend. Looks like I'll be getting the adapter too. The tank held solidly on my back without any shifting. Instead my problem was getting the tank straight with the plate at the start. I kept securing it at an angle.