I built a rack last year out of 3/4" OD tubing and researched all my options to mount to the gutters in a clean, strong and simple fashion. I cut and bent 2" x 1/4" flat iron at about 6" long with a 30 degree bend in the centre. Then I fabbed a bolt tab from 1" x 1/4" about 1 1/4" long, drilled a hole for the bolt to go through, and welded them to the 2". I then took some 16 G sheet steel and cut into a small triangle, then bent the bottom 1/2" to a 90 degree to tuck under the gutter. I cut the heads off four 5/16" x 3" bolts and welded them to the 16 G tabs. The bolts and tabs go up through the 1" x 1/4" tab with a nut and washer on top. It has worked great so far without any rattles and has never come loose. I also stuck some adhesive backed foam tape along the bottom edge of the 2" x 1/4" so it would stick and not scratch. I can take a few picks and post them if you want. Let me know and hope I could help, good luck.
