I think your drop outs has 2 sets of holes. I recently mounted racks on 3 Trek FX bikes this past spring, and I think I remember seeing extra holes and thinking, cool bikes, good to know for future commuting needs. if not, just double up. there's a California shop, like an official Trek accessory store, where I bought one of the racks, they seem pretty well informed and can hook you up with the right fenders.

http://www.trekbicyclesuperstore.com...SiteSearch.y=9