Wasn't sure which hatbox thread to post this in, but after reviewing the three threads I found on hatboxes, I decided this was best/most appropriate (even though this has become a vintage hatbox thread, the others seemed more specific.)
So, a custom hat should have a custom hatbox (even if crudely made). This is a couple of 36"x48" corrugated plastic sheets from Lowe's lined with some scrap black fabric (hat circle from the hat shipping box) and held together with glue (fabric)and packing tape (box). I used velcro to keep the lid closed. Works for me and keeps the hat safe until fall.
I bought a hat (that was not original to this box) and asked the auction house to keep the hat box and ship the hat in a proper shipping box. They did neither. They just covered this box in packing tape and sent it out. Maybe a good thing as it sat in the rain on my porch for a few hours. The hat is fine, but the box is not. It's one I've not seen, so it's a bit sad that it is gone.