Personally, I prefer to sew everything. Otherwise, the piggies tunnel under the fleece and it is soon in disarray in short order. Plus, the sewn mats seem to be easier to vacuum and to wash.
If you sew, it has been recommended to me to put a piece of the U-haul blanket between the two layers of fleece with the idea being that the fleece wicks the urine away, and the U-haul layer absorbs it. Once sewn, how much easier can it be to remove the pad, shake and brush it, and toss it in the washer on warm?
If you aren't planning on sewing the fleece, then you may need all of the two yards and attach it to the coroplast with binder clips.