Newby Fender Question

Well...things are going along fine...but I'm getting ready to do a cut on my fiberglass fenders....Here's the profile...
I need to trim the fiberglass fenders to finish them. A couple questions...
1. What is the best way to cut this curve..belt sander, jig saw or other?
2. The fenders will be painted...what grit should I sand them to....the gell coat seems pretty slick.
3. Is there a preferred liner for the wheel well? I was thinking about just getting a can of spray undercoating...but maybe something else is better.

I need to trim the fiberglass fenders to finish them. A couple questions...
1. What is the best way to cut this curve..belt sander, jig saw or other?
2. The fenders will be painted...what grit should I sand them to....the gell coat seems pretty slick.
3. Is there a preferred liner for the wheel well? I was thinking about just getting a can of spray undercoating...but maybe something else is better.