TulsaJohn, P clamps was what I was thinking about using. I have a set of NeedleWork Panniers to go on the front and they fit perfectly. They were originally sold (I think also made by BG or Robert Beckman) and fit fantastically on the rack as you stated. I'm a little concerned with waterproofing as you mentioned, but other than that they seem like an awesome set up, even years later.
I'm curious, do the P clamps hold the rack well and tight? I was wondering if they might slide/move around or break over time? I'm planning on doing some long tours and maybe even around the world so wondering if it might be best to sell this BG rack and NeedleWork Panniers and get a Tubus rack instead with Ortlieb panniers.