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This is for those of you who may frequently ship sousaphones around - have you found the "perfect" size box to ship a BBb Conn 20K sousaphone? Or do you have to get something and cut it down, or combine two boxes?
My quick measurments say something around 42" x 32" x 18" should do it, maybe a bit bigger to allow for bubble wrap or other packing. I don't see anything like that in the box catalogs I have searched so far. Double wall material or nesting boxes would be great.
I will be shipping via Greyhound (from California to Chicago) and have had some moderately good experiences with them over the years.

Any ideas?
TIA.

Of course... in a case would be my preferred method of 'Going Greyhound'. However... I've been known to safely send a sousa by first wrapping the bell in bubble-wrap, a sleeping bag, or old Indiana blanket. Then... nesting the body over the bell and wrapping it again with the same type material. The final wrap can be just any cardboard you can make go around the horn. It doesn't necessarily have to have nice neat 90 degree corners as long as every thing is covered with a few layers of padding/cardboard.

A couple of cheap foam mattress pads from Dollar Store will work. Or... go to Goodwill and buy a foam rubber mattress.

We have two tuba-sized cardboard boxes at home. The one I can easily get to is 48 x 30 x 24; the other is about the same size. They can be yours if you want them. We're near Los Gatos, about an hour south of you (assuming you are in San Francisco proper); PM me if you want them, and we figure out a way to get them to you. Maybe meet halfway, for example at James' tuba store in Menlo Park?