Keep in mind that a spring, although necessary, will add height to the system. Also, you want a good amount of antenna to extend past the roof line. Although not necessary it will increase your range and cut down on feedback. I went with a lil wil magnetic mount on my roof. The mount does not extend past the factory roof rack rails so clearance isn't a problem. I think the antenna is about 3 feet tall. It's a whip that can be taken out really easy. I just keep mine under my rear cargo mat. I used to use fiberglass antennas and never got any performance out of them. I had a tuned radio and tried 3 different models. They're heavy, swing around a lot and can break. I broke one and shattered the inside of another and they were both on mild trails. So mild I think I had hit the antenna harder on my garage before. I think that on a 4runner it's too much work to make that mount work, spring, bunge cord, tennis ball and a bunch of screws.
http://www.wilsonantenna.com/lilwil.htm