It's tough to ship a backglass that's starting to come apart. Do you have photos?

I would not do packing tape.

Triple thick won't solve delamination. You'll need to use super glue to adhere the paint back onto the glass.

Crushing the paint flat invites issues of possible damage to the delaminating paint. But that depends on what the state of it is. In some cases, it might work.

I might suggest shipping the backglass face down in a heavy duty box, and try to ensure some way that it doesn't get transported sideways or upside down.