Darn, that's rough. I had a tough Yazoo Mills tube similarly crushed by the USPS. Thankfully, everything worked out with the insurance claim and luckily the seller had one more copy of the poster that I really cared about.
However, I've had (non-poster) packages similarly destroyed by UPS and FedEx. So I'm not sure there is much you can do other than pay for insurance and hope for the best.
As mwright mentioned PVC tubes are a good option if the additional shipping cost is justified for the items in question. I haven't shipped in PVC myself, but I have checked a large PVC tube of posters on a flight from SFO -> SEA. And if you've seen the way the baggage handlers at SeaTac treat luggage, this was a far scarier prospect to me than USPS/UPS/FedEx. When I picked up the tube in baggage claim I saw that it had been opened and a sticker left noting that it had been examined by TSA (it looked like a pipe bomb I guess?). My heart sunk as I feared that posters would be missing or damaged. But everything was fine! How is that for a ringing endorsement? If PVC can withstand the TSA, then surely it can hold up to USPS/UPS/FedEx.