I used 40 lb. roofing felt (paper). Cut the strips 3 inches wide, and folded them over 3 times, making them 1 in. wide, then cut the lengths. That makes them a bit wider, but did not seem to hurt anything. After the tank was installed and clamped down, I also wedged rolled towel in the voids between the tank sides, and tank end and the tub to keep dirt, rock, sand, limbs, sage brush and etc. out somewhat. Jim