I was planning to just ship my box on its own unless it will be cheaper to use a flat rate box. I don't have a legends box but it is the same type, a 10x4x4 mailer box from Staples. I have a lot of nice foam to pack with from work, if it is good enough for packing sensitive parts worth thousands it should be OK for my car.
I was curious how most people ship when only sending 1 car. Always seems when I am shipping packages I find out later that I could have done it cheaper with some less obvious option.