Originally Posted by
kevmcd
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I think I am back to the Amtrak box and if I get stopped I check-in I will figure it out.
If you change your plans so that you can fly in and out of the same airport and if you are trying to make a huge box with custom dimensions for your bike to fit in a 115 inch box, presumably with a box that size you clearly must have access to a vehicle that will hold something that big. Home Depot sells Coroplast in 4 X 8 foot sheets. You could make a custom size box with two sheets. Would be more costly than a Amtrak box but should be able to take a lot more trips.
I use a pizza cutter to score Coroplast (or cardboard) before I try to put a crease into it to fold it, that makes it easier to get my fold exactly where I want it.