I have my GPS antenna behind my instrument cluster, with the magnet holding it tight in the metal bay there. I get 5-7 satelites on average in downtown Chicago, which is wuite well between all the highrisers. if you don't want to remove your instrument cluster you can get there from the bottom too, just remove the kneebolster below the steering wheel.
See the links directory at the top of the RNS-E forum for links to pictures and instructions.