One sheet of plywood, 2440x1220x9mm (shuttering ply is fine), is enough to line the inside of the cockpit. I used glass fibre to finish off the curved rear corners, but the designer cut triangular wooden fillets and bonded them in.
http://www.sammio.co.uk/Gettingstarted.aspx
Looking very nice now by the way, you'll have a car to be proud of in no time.
