I'm using 4" black PVC in roughly 18" lengths to store tools, lube, tubes, etc. I have them mounted to the underside of my milk-crate and the entire unit is modular, in case I lay the bike down, the tubes and/or crate will snap off before the frame is bent. Then I just zip-tie it back and ride on. Seems to work so far. Even at speed (+70mph), no wobble, no vibration. Good times.