Boat seat foam and glue We use Sunguard polyester in everything we do, boat covers get a different thread that lasts the life of the canvas.
Also, regular foam will mold like no tomorrow. If a customer wants to spend money and make sure it lasts, you need to use flow through foam or dryfast foam. Expensive... yes, but well worth it.
Use mesh under the cushions or vents if mesh isnt an option.
Stainless staples is a given even if its a freshwater boat.