I've though about doing this for a few reasons, we don't have mud or snow problems here. I have been thinking about using the felt ones from the nearly extinct contour/mystique, or possibly the focus. I would never, ever, think of using metal for them. One of the purposes, these days, is to reduce road noise, and the felt ones would be best at that. The plastic ones can be easily reshaped with some heat, you can use a mapp torch if you are very careful. I used mapp torches to fix bumpers, much faster than electric heating. Some liners are much easier to work, the taurus ones are pretty thick and rigid, some gm ones are flimsy and real easy to rework. If you want something new, the liners on a dualy truck are huge and cheepish.
Here is the part # for an older ford for example The list price is old, but shouldn't be that much more, also note that you can deduct at least 25% off for shop price.

To attach, the inside is pretty simple, just drill screw holes, if you want to be fancy, screw in from the engine side and use plastic nuts on the inside. (or you can go to a junkyard and steal the hardware from a bmw) On the fender side, a bit more tricky as you really don't want screws showing. After you have the inserts fitting reasonably well, I would make brackets that I would epoxy to the inside of the fender. These brackets would hold screw clips that would be beyond the lip of the fender, making them less visible.

I also hate visible antennas, there is so little need for them these days, especially as radio dies. I know hiding the antenna would require hiding the hole in the fender, I've already plugged mine up. If you have ever noticed the aerial on a ranger is spiral, that is to reduce wind noise.