Vince and Kernow: Thanks guys sounds like a good suggestion and yes you are right it would have some built in drainage. Only problem would be the like about "some good glassing" - hmmmm - not my strong point
Would you suggest laying the marine ply in first and then applying the CSM over the top, then resin and build up in layers?
Also how would you recommend preparing the surfaces of the preexisiting gelcoat on the deck. Is it OK to rough up with some coarse 'ish wet 'n' dry and then clean with acetone or do I need to go down to the base resin?
Finally the final top coat of gelcoat will need wax solution to turn it into flowcoat but what's the best way of applying it, brush - roller (- plaster's trowel
Thanks again guys