When my 1988 Catalina 30 is closed up for a week at a time I notice a strong smell of diesel when I open the hatch. The boat yard has checked for leaks and has found none. There is no diesel in the bilge. When I'm on the boat for the weekend there is no smell after being open for a short while. I suspect the diesel fumes are being vented into the cabin somehow.Any thoughts? Anyone have this problem before?Thanks