as mentioned hire a carpet cleaner.not a machine, i mean a man with a van. can you pull the upholstery or is some attached? formerly i did some carpet cleaning. one of the best methods is to spray a cleaner on the moldy areas, put down a clean white cotton rag, and beat it quite firmly using a tamping brush. you will be amazed at how much comes up just doing this.. never scrub a stain with anything. that’s how you set the stain. the truck mounted carpet cleaner can add super hot water ( steam ) which will get that out. much better if you can remove the upholstery or get the boat to them. this kind of thing isn’t happening in a marina