Looking at uline catalog for mailing tubes. USPS Priority provides mailing triangles for free which is great for large items. For smaller roll up items 24"x 15 perhaps a 2 inch or 3 inch tube would be good? What is the correct way to roll up the item? Against the curl? When I try that it seems I get dimples in the paper in some areas. (I practice on discarded non printed paper of the same media type I will be mailing. For roll ups do people put a layer of tissue paper on them? I suppose I could roll up with the image side out to make it easy but that would not do much to get of the curl. Then put tissue paper on the outside so the print would not get damaged.
I googled how to roll up a poster and I got this youtube video.
http://www.youtube.com/watch?v=2DE6-IrsLFs