I own a pickup truck and got a bit tired of all my gear (masts) being diagonal in the bed of the pickup. So, I built a 'conduit' holder (much like what electricians and plumbers have) and mounted it to a bed rack made by Thule. The rack is called the Xsporter Pro and has 2 channels on the bottom and top. The goal is to store most of my masts in the truck for the season. Hope this helps some one someday.
1. You'll need a conduit kit + a 6 inch PVC pipe.

2. The conduit kit. Note the U-bolts are for mounting through a rack cross member. I didn't want to drill holes in the Thule 'channel' aero rack.

3. Glue the end parts onto the Pipe. I opted for glueing and not drilling holes.
4. Since I was mounting the PVC underneath the rack (Wanted space for a board on top), I had to use carriage bolts with the square portion to fit into the Thule channels. I built an aluminum bracket to 'hang' the pipe. Using a vice, blow torch and grinder, I was able to fabricate a bracket.

5. Here it is mounted to the rack

6. Mounted and installed. It doesn't stick out the back too badly.

7. I have mostly Ezzy RDM masts in here (3 mast sets total) . I have room for more masts to spare.

8. Another view.

9. Stickers for effect! I also have a small carabiner to prevent any accidental opening of the door.

I hope this helps someone somewhere someday. Let me know if you have any questions. Hope this contribution was worth it.