I think the ultimate best storage would be a cabinet with panoramic width drawers (libraries have them). But completely impractical for me.
What HP5 film are you using?? Is this 9.5" aerial? If so, that polyester type base is unlikely to take a curl and I'd lean toward rolling them up (well that's what I do anyway). If you've got 10" HP5 on acetate base, then I'm jealous.
Let me know if there is any help I can give. I have lots of gears and assorted Cirkut stuff.