My wakeboard does not fit in my trunk because i have subwoofers, and when it was in the backseat it was akward and unsafe to carry passengers. So i devised a way to hold my Wakeboard on the roof of my car. It hold's it securely, goes on and off easily, and can be made (in my case) with materials that i have around the house and shop. Good luck.
Step 1: gathering tools and materials
-apropriate hardware (4 screws and nuts and some washers)
-and a saw (i used a table saw, but use what you got)
-wood, i used 1/2 inch plywood for the blocks and i think a 1x3 or something for the tops.