It's quite a task to ship any framed pastel. I usually ship them with glass unless the show has specified plexi-glass. Thanks to an artist we met in Winter Park, Florida, I've found an less expensive alternative to the Airfloat boxes. This is especially good for larger pieces. Those Airfloat boxes are great, but when you get up there even a little bit in size they are pretty pricey.
So here's what I've done; First purchase a box that is approximately 4 inches all around larger than your framed piece and about six inches in width or whatever width will accommodate your piece and two, two inch pieces of the foamular. You want it to be snug in the box. Wrap the framed piece in the thinner bubble. Bunch up some bubble on each corner to give extra protection to the corners.
Go to home depot and purchase Foamular insulation material. It comes in 4'x8' sheets. Have them cut it so you can get it in your vehicle. When you have it home, you can easily cut it with a utility knife to the size you need to fit your box. You want to have two pieces that fill the box and you can slide your pastel in between. The beauty of this material is that it's rigid, will make the pastel snug in the box, protect it, yet not be a mess on the other end. When you ship a piece to a show, like a PSA show, the shipping agent does NOT want to deal with nurdles or anything messy that is hard to repack.
I've had good sucess with this method and plan on using it for the larger pieces I have to ship. You can usually find a box company locally that has some standard art boxes that have thicker cardboard. I also try to save boxes from ready made frames or anything that comes that seems like it could work for me. This of course takes up space! Yikes! Good luck with shows and shipping. Feel free to email me for more info!