Modern racks for old 10 speed?

Hi All - I'm trying to set up a 70s Dawes Galaxy to do some bike camping this summer. I'd like to put on a decent modern rear rack, but I was wondering if there are modern racks that work better than others on older bikes. My bike frame has rack mounting holes on the dropouts but not on the seat stays. Should I just get a rack that is made for seat stay mounting holes and rig something up with p clamps? Or is there a better solution?

Thanks,
Clark