It is usually better to store the canvas assuming it will be subject to less extreme conditions. It can get pretty hot under shrink wrap but it can also get hot in an attic. Either way should clean the 'glass' with fresh water ( and very mild soap if really dirty) to get any debris off.You can apply a treatment made specifically for your glass to help keep the protective coating in good shape. Plexus is one option. I use Aerospace 303 protectant. Make sure its the protectorant and not the waterproofer or upholstery treatment. The panels should be rolled not folded and should have a protective layer of material to keep the plastic from coming in contact with itself. Old bed sheets work well.
If you need something else to do, get some lubricant ( I use zipper lube) and treat the zippers and snaps