I've had a couple of trunk racks, one of which i used to haul two MTB's from WI to Arkansas. The thing I learned is that you really have to learn how to stretch the straps tight, position the strap hooks so that they do not slide (and thus introducing slack to the straps), and secure the loose ends so that the strap can not wiggle backwards through the buckles. They are a pain to secure properly, and the ones I used always slightly creased the sheet metal with the top hooks.