I use PVC pipe... 4" or 6"... cap on one end (glue on) and on the other end the flange and screw in cap.
To screw or bolt it to trailer/truck/whatever I first drill the holes for the bolts/screws (usually 1/4") then directly opposite each of those I drill a 1" hole with a holesaw. This lets me use a socket wrench to tighten the bolts down. I plug the 1" holes afterwards to keep rain/wasps out of there. Easiest way to do that is to cut 2" off the end of the PVC pipe, then cut that into 2" wide pieces. You end up with 2" X 2" pieces that are curved like the pipe. Use PVC cement to glue them over the 1" holes. Three holes are plenty for 6' to 8' length, using 1/4" bolts.
You end up with a watertight storage tube that the poles can't get out of, lasts practically forever, and they won't get damaged or be subjected to the elements. Also, very cheap to make. They are easily painted with spray paint.