Fabric needs to breathe, so I don't think plastic is a good idea. There are always cautions against storing fabric (for a long time) in plastic tubs. Finished quilts are better stored in pillow cases than plastic bags. If you are worried about the boards, I would wrap with muslin as suggested. Since you are not going to quilt with it, you can get a bolt of inexpensive muslin from JoAnns or WM.