Yep, I used a length of foam pipe insulation. I inserted the original fender mounted antenna inside it, taped it in place and then carefully slid the whole thing up under the dash where I used more duct tape to hold it in place. It's been there for about 10 years now. The reception is great and distance wise it seems to get clear reception the same as if it was mounted externally.

Of course I had to fill the hole on the fender with something. This was my solution ... LOL.