Harbor Sales Service
My friend and I have made quite a few smallish orders from Harbor, and they are outstanding. But, here is my standard advice. CALL THEM. The web site is not intuitive (IMHO) for what most of us do. What you want to do is buy 4' x 8' sheets, but have them cut for shipping. I have them cut each sheet into 2' x 4' pieces, but the UPS shipping rules also allow 32" x 48" pieces (thirds). The reason to call, rather than use the web site is to get the flutes in the right direction. Out of a 4x8 sheet, you get 4 2x4 pieces. Maybe you want 2 with flutes in one direction and 2 with flutes in the other. On the phone, that's a piece of cake, they do it every day for us Spadders. My memory is that shipping is free (over $25 ???), but there's a small charge for the cutting.
The best thing about Harbor is that the packaging is perfect for storage, plus the coro they sell seems to stay flat forever.
Call them. I am sure they will take really good care of you. They know we are building model planes.
Don't forget to add a couple of rolls of 5 year vinyl!