depending on which antenna you have, you just put it on top of your dash and then you won't have to worry about cable routing from outside. I have one of the low profile Terk ant in my 02 sitting on my dash and it works flawlessly. You also have to look really hard from outside to see it whereas mounted to the roof, it's a dead give away to a hoodlum that you "gots a system in yo ride".
just my . 02 worth... ymmv
Jim