My suggestion is to get a sheet of something good and waterproof, slightly larger than the quilt, and attach some cute button to it in the corners and (depending on the size of the quilt) in a few spots on the sides as well. Then attach little tabs to the quilt in the right places, with buttonholes in them- this means that the quilt can be used in any situation (without the backing buttoned on) and can also be washed, plus it means that it will stay in place on the waterproof backing, when waterproof backing is called for. (Maybe made a little barrel shaped bag he can roll the tarp bit up into to make sure it is identifiable as part of the set, and does not get misplaced/ loaned to his friend who is moving house, changing the oil in his car, etc?)