I've done one piece cues using the PVC pipe as mentioned before. I usually will tape two of the 'triangle' shipping cartons together and put the PVC pipe inside.
Anytime I ship a cue over $500 value with no case I usually use a piece of PVC, even if it is a 2 piece cue. A few bucks investment sure prevents a lot of headaches in the long run. I usually ship USPS and it seems the Priority Mail triangles aren't near as strong as they used to be, but the FedEx ones are still very hefty if you are going that route.