SeaDek is made of the same family of foam (EVA) as our coolfoot line of products http://www.coolfoot.biz and is easily cleaned with any orange cleaner. We recommend a sponge and if the stains are really tough, the scrubber side of a kitchen sponge. EVA is a great product and is usually easy to clean.
We use a 3M product for protecting the coolfoots from fading called Scotchgard-Outdoor Sun & Water Shield. It comes in a spray can and works great.