This would do, and cheap.http://www.ebay.co.uk/itm/CAMO-CAMO...Goods_Camping_Accessories&hash=item484d57bee9 Parachutes are not waterproof until they have had many fires under them, to build up a layer of tar. That said, they do look good.
it does depend on what you mean by large tarp and also where you'd like to site the tarp, if it's a fairly casual setup that you're just going to do now and then the costco tarps are great.