The easiest way and what Ive been doing for years is to first carpet the piece. This will work as padding to avoid any defects in the surface and to also eliminate possible tears at the corners. The using 3M 90 spray both the vinyl backing and the carpet, let it get a bit tacky then put them together. Wrap all the sides and make your needed angle cuts at the corners. The using a nuematic staple gun staple it underneath. A regular staple gun would work, but would take forever and is a Real PITA.
Hope that helps some. Cars that Ive done back in the late 90's are still holding strong.