So would you recommend boxes over tubes? My instinct would have been for tubes so what benefit do you find with the boxes, is it just that they are easier to store?
I personally do not understand the point of those mylar sleeves, unless you feel the need to look at your posters over and over again, which I don't.
I have a system that works for me, as we all do.
Everything that is
not US one sheet, quad or B1 size goes into flat files. Perfectly organized by countries and sizes. Folded quads in one or two drawers, German A1s and medium French in another, numbered prints by stacks of two in 5 drawers (I have a lot of this crap), large Italians, large French, Polish, B2s, Star Wars, etc... all in their respective drawers.
All
rolled one sheets, quads and B1s go into square tubes. I first put the posters into tubes by year of release as I get them. Those tubes can be seen at the bottom of the picture. I can put 35-40 posters in a single tube. Once a tube is full, I transfer the posters into a sleeve for extra protection from insects or water (you can see it in the picture) and into another tube where they will be until I die. Those "final" tubes are in the background. Works for me.

T