Has anyone built a rod tube out of PVC? looking to store 4-6 rods on an fj cruiser.

Years ago I built one out of a large size pvc ( like 4 or 5 inch diameter) lighter weight pvc (not schedule 80).   I installed a pvc pipe cap on one end.  I installed one of the threaded caps that a plug screws in.

If you are like most of us, you have several cardboard mailer tubes in the rafters. I know I will need them some day!

Yes, just cut to the desired length. On one end glue on a cap. On the other end glue on a female threaded connector, then install a screw in plug after you insert the rod. 

If I were going to mount that on a vehicle I would want to be able to secure that as well, so I'd probably try to come up with some type of hasp or bolt type lock at the threaded plug.