I am not sure it matters, but I always store my glass flat. For all my lams, I get the 4 inch white (with holes in in) drainage tubing from lowes, glue on a back cap and put a nob on the front cap and keep all my lams in there.
Because I have limited storage space, I tie a short rope to the back of the storage pipe and then screw that rope into the wall, a longer rope on the front of it and srew it to the wall....then when I need a lam I can just swing that pipe out, pull the cap off and grab one out.