. . . Box around the 30 x 40 with a sheet of foam core on the face of the print, then place that box inside a separate box and then hope it's not destroyed by UPS. . .
Send by FedEx Ground or FedEx Home Delivery, or Priority Mail, and the box will arrive much more in the shape it was shipped in than if it goes UPS Ground. Stated based on having shipped over 50,000 packages in a previous business.
When I ship stretched canvases, I am always scared to death. However, I haven't had a single problem with FedEx Ground/Home Delivery/Priority Mail. I don't even insure the packages for more than the amount they let you insure it for without extra charge. I decided to go the route with packaging that would be adequate for a normal person moving a box around - but certainly less than adequate for what the shippers recommend - and substantially less than adequate for what UPS Ground would need for packaging. I often have a whopping 1" of packaging material around the canvas, and use a single box, but do use extra pieces of cardboard.
Somewhat crazy choice, but I made it for several reasons. The cost of a package goes up substantially when the size of the box goes up (dimensional weight.) The money I save by not paying for insurance should balance out well for the cost of re-printing a non-original piece of artwork that can easily be replaced. (Someday something will get damaged.) If something happens to a package, I can easily tell the customer it's taken care of, and not have to fight to get an insurance claim paid when they're going to say it was inadequately packaged unless a ridiculous amount of packaging is used.
For the material, I use a combination of foam in roll format and bubble wrap. I typically foam wrap the canvas piece, and tape on a single wall piece of cardboard on the front and the back. Then, I use bubble wrap to fill the rest of the box. This way, bubble wrap isn't going to push on the canvas and make it looser or create dents being pressed on the stretcher bars.
