Thanks for all the suggestions so far. Please keep them coming. I made a fabric liner from some raincoat vinyl backed nylon lined with denim. The fit was wrong. I didn't leave enough room for the corners where the uprights go through. It took almost an hour, so back to the drawing board. I did order 4 shelf liners from Amazon. If they are amazing, maybe I'll "bite the bullet" and buy more. I haven't been to the dollar store yet to look at placemats and foam board. The plastic canvas may work, too, and I will also try the doubled freezer paper suggestion. You all have such creative minds!!!