When I shipped my PIF'd tubes of cream I made a custom box that just fits the tubes plus a little bubble wrap, but if the postal guys drop a 30lb package on top it's still going to get squashed.
I kept some of my small Amazon boxes and air bags to fill them just so I could PIF stuff. I've been on the receiving end of smashed stuff too many times from when my Mom would send me cookies and stuff that I try to protect my shipments the way an online retailer would. It costs a little more on my end to ship it but its worth it when it arrives in good shape.
The bubble wrap envelopes tend to get smashed easily.