I recommend the Problem Solvers seat post clamps with rack eyelets. I'm using that along with P-clamps down low to mount a Super Tourist Disc rack to my road bike (got the disc version as I'm hoping to build up a disc commuter in the future). It really works great, especially with the Topeak MTX bag with fold-out panniers. I ordered all that off of Amazon along with a cargo net tie-down thingy which I've actually only used once to carry one of my son's trailer wheels to the bike shop.