Originally Posted by ragamuffin

I do slipcovers and the proper way to do it is to get a piece of foam and wrap it with the poly one or two rounds, square the corners but cut the excess off. Using a white threaded needle, use large stitches and sew the poly closed at the side and all the corners. You could stop here, or you could cover the poly with a muslin or an old sheet, and again sew the corners and sides shut. This way the top fabric will not "walk" and go down over the edge. I would like to see you put
some cording in but that is up to you. You could put a zipper on one side so you could remove the cover to wash it. If you have any questions, just pm me. Love to see the outcome.