Hi. 1st post. Just picked up a Yak Skybox21 for my 07 Sienna for use w/ factory rails. In garage, clamps tighten nicely, but there seems to be up/down movement on right/left side due to curved factory crossbars. Seems that this wouldn't occur w/ Yakima (or Thule, etc) straight aftermarket bars.
Anyone else running a skybox21 on factory rails? Is there any movement when driving?