I have had my best luck with tarps at Costco. They sell twin package of 12 by 16 foot tarps for about $20. When using tarps, you will find it easier to use 2 12x16s than a 12x32. It enables you to slide one over the other and make a better fit. The smaller ones also weigh less and are easier to fold and unfold. Besides, it will enable you to use them other purposes as well.