Already have the frames on the bike. I made them earlier in the year with the help of SteveH who did the welding. As for fixings, I'm going 'simple' as it fits my mentality and the panniers will bolt directly to the frame at 3 points. I plan to pass the bolt through the pannier from the inside out and lock it in place with two nuts which will act as spacers between pannier and frame.(something that's required cos when I made the frames I made them 10mm too narrow to clear the indicators. Oops) this should allow me to pass the remaining bolt through the frame and secure with a nylock nut.
The bit I'm puzzled by at the moment is how to fix the lid without welding. If I hinge them with the bolts poking out then the nuts could be undone, if I go the other way then the nuts will foul the box :-? Heyho, the fun of being an inventor.