The Gowesty site (gowesty.com) has a link to Yakima which will spec out
the rack for you but it ain't cheap. I have also seen a homebuilt kayak
Westy rack description somewhere on a late night brain-drain surfing
session--I think it was on Alastair Bell's site--which sounded good. I
prefer Yakima racks for mostly speculative reasons--I think the round rack
bar is more heavily built and will bend less easily than the square Thule.
Compare their maximum load ratings. Also, I THINK you can use standard
3/4" pipe for the Yakima rack bars instead of the plastic covered and much
more expensive stuff they sell. In fairness, I have only ever used Yak
racks. They sell rack holddowns for every manner of thing and if you have
the time and inclination you could study their Kayak system and make up a
pair of custom supports and buy some 1" strap ratchets to hold the boat
down with for much much less. I do like the Yakima towers and carried
heavy loads with them--just make sure they are well tightened!
                          Good luck!                Sam