I just got one of the large Fuel Belt ones, and it's going back.
I was figuring I'd have to protect my frame and head tube spacers with some of that plastic luggage protector stuff, so marking isn't my concern, but I think you'd definitely want to protect any parts that the box came in contact with.
Maybe it's because my head tube angle is too shallow, but there's a large differential in how close (or far away) the bottom velcro strap hugs the head tube, vs. how close the top velcro strap hugs the head tube. And it seems like the stem clamps would catch on the zipper and either interfere with steering, or pull the box side to side.
Are there any of them that are made with an angle in the front, so they fit uniformly?
Speed comes from what you put behind you. - Judi Ketteler