I don't need a weight box for anything I do but suggest you could also check on Bayrite if available in your area. This is a weight material used in drilling mud, IIRC it weights about 36lbs/gallon. While it packs down in a box it is removeable if that is desired. At over 7000 lbs /cu. yd you should be able to fill your weight box appropriately and leave the turf tires unfilled.