Amazon has this PI Store Waterproof Car Roof Bag with Protective Mat marked down from $99.99 to $19.99 and it ships for free with your Prime Membership or any $25 purchase!
The waterproof Cartop Carrier keeps your cargo dry by applying 100% waterproof Nylon fiber. Robust Kevlar threads, heat-welded seams and reliable zipper together provide triple waterproof protection to your luggage on a road trip through rain, wind, sand and snow.