If you]re going to cover a seat with leather or suede use a 2 or 3 mm skin foam
first cut to desired shape of the top seating face and glue it to the plastic with spray upholstery adhesive { available at motor accesory shops )
This will help achieve a perfect unblemised final surface when glueing the leather cover on top ,
also the foam prevents the Kashi drill holes from showing through after a period of time