Dave, surprised you have not had an answer to this already. Many of us have TT panniers on a 1200. As you suggest using a TT frame for a 1200. Mine have done about 20,000 miles and suffered a few falls and still fine. I think it's a 35L and a 40(something) on the RH side. Totally waterproof, which can not always be said for the GSA ally panniers! Go for it!