Cars are complex machines, and fitting them safely is important. Yakima’s and Thule's fitters are updated live by the manufacturer themselves. If you have any difficulties feel free to call instead and we’ll help you through it. Adding accessories in the fitter is fine, but we often offer a wider selection on our website and many accessories fit both types of racks. Perhaps a Thule box on a Yakima rack is what you need. Neither fitter will display the other manufacturer's accessories.