Hello, Rich.
Here are some suggestions. Good luck and don't forget to wear your safety goggles.
1) 1 1/2" ID Schedule 40 PVC is the best.
2) Use a 3/8" bit to make the holes in one side-wall of the PVC pipe. Don't worry about making holes in the other side wall. PVC is soft.
3) Use 3" #2 Phillips-head, coarse-thread screws. Any type will be fine such as galvanized, black drywall, decking, etc. I don't recommend stainless steel, though. Galvanized or decking are good for outdoor storage.
4) Use a 6" Phillips-head #2 bit to screw down the PVC. Make sure the PVC pipe is resting securely against the wooden frame when you fasten it. The 3" screw will drive directly through the other sidewall and into the wooden frame. The top of the 3" coarse-threaded screw will rest securely against the inner side-wall of the PVC pipe.