If you want to assemble your own system, check out Groucho's offering on page 2 of members' storefront, heavy duty roof clamps and cross members, I have four complete sets of his clamps and cross members. Very strong and adjustable to within 3 or4 inches of the roof or raised to 5 or six inches. You can carry sheet goods for construction and other big items securely. Then you can, when the situation demands, add a roofbox, or a traditional roofrack of virtually any size. May sound like a belt and suspenders approach, but you have versatility, strength, and don't always have to ride around town with a roofrack loaded with back country gear.