renewing door card

Hi could anyone help, the door card on the drivers side is very soggy due i think to poor seal alignment ,but as i intend to sell the stainless speaker covers and renew the pvc covering ,the question is do i use hardboard again or do i use a thin marine ply .If anyone has done this, advice would be most welcome as this is a sticking point and until solved i cant get on with the job in hand .Thanks Glyn

 Good info here I used this method very successfully

How much do you want for the stainless steel covers?