satellite radio in semi truck

hey guys need a refresher, have to reinstall a sirius tuner in a kenworth and naturally no metal in the roof to refract the antenna signal, does the old method of putting a piece of metal uner the fiberglass where the antenna sits apply? ive been away from audio for a couple years just doing starters and seatheaters and such, and i remember they used to recommend in a boat install to put a piece of metal(aluminum foil i believe they even said) under the spot where antenna will mount,m does this still work? thanks guys (and girls)

top of mirror mast works well, done that a handful of times. but just have them get the semi sirius antenna. works a lil better.