I have a 1978 Chris Craft Catalina with an interior floor I will be replacing.  It is not secured and just rests on a ledge under all edges.  It is approx. 7ft by 24 in with a hinge in the middle to allow access to the bilge pump under it.  The last time I replaced it I used plywood and applied several coats of varnish on both sides and all edges.  It lasted several years before moisture got to it.  I am open to alternate ideas but I'm also fine with just getting plywood again and using varnish.  The varnish looks good but doesn't last forever.  I could go with fiberglass resin but I don't want it too slippery either.  Any ideas?
				
			