I have made 3-4 in the past. I have bought a couple of large dog beds at Costco and
made new slip covers when the old ones wear out. I buy 2 yards of upholstery fabric on sale at Joanns fold it in half and sew the side and one end up and sew a heavy duty zipper into the other end. They work great and the dog's seem to enjoy them. it's nice to be able to unzip them and wash the cover when the get dirty.