I'm not sure you need to get into the fender. If you have all the plastic corrugated strip out just buy a new antenna and get a friend to help. With no antenna in the hole, put the new plastic end down in it with the stereo ON, then have the friend turn the stereo OFF while you push the plastic strip in. The motor gear should catch and suck the strip down. Of course you have to mess with the mount but that should be fairly straight forward.

85 4Runner 22re, mostly stock. Over 340K miles(SOLD for $4000 7/06)

98 2.7 4cyl 4Runner Bone Stock perfect 200,000 miles (alright, it has a HG and clutch in it's past)