Since this thread has been ongoing for a long time, I'll give my 2 cents worth. I have made over 40 totes. I use 2 layers of the plastic canvas and enclose it with batting and a sleeve. I do not take it out to wash!!! It makes the bag totally washable. I've washed my summer/fall bag at least once every 2 weeks since June --- only changed out so I could use my Christmas bag.
My husband cuts me thin masonite pieces to fit each bag and rounds the corners. I have also used the plastic canvas. A couple years ago I was at a library book sale, and there were hundreds of books in a trash bin out back. I took some large books and used the hardcovers cut to fit. They were great!
I also use the back of worn out cutting mats when the front is too damaged to cut on. It works just as well!
That is a great idea. I have 2 that are almost worn out. Thanks for sharing this.