Cushions on deck

I am currently making a deck for my 14ft v hull lowe 1467 boat. I put the structural aluminum tubes and plywood on top of it. Now I would like to add some cushions/foam on the sides of the hull to make this area more comfortable for seating and laying around in the front of the boat. I put some pillows just to have an idea of what it would look like (see picture below) as a test. Now I need to buy the foam and put some waterproof tissue on top if the foam/cushions so I can attach them to the deck and leave them permanently on the boat without them taking up water.
Which kind of foam and tissue would you recommend for that?

On a cabin cruiser boat that I've been building I have also been thinking about how I would make cushions for the bow area.

I have not actually tried this yet, but my plan was to buy a cheap memory foam matress and cut my cushions from it.
https://www.amazon.com/Sleep-Master-6-Inch-Therapeutic-Mattress/dp/B005G02ESA/ref=sr_1_1?s=furniture&ie=UTF8&qid=1426878487&sr=1-1&keywords=foam+mattress

Then I was going to cover them in waterproof vinyl. I don't know exactly what you have in mind, but I was going to make 1/4" plywood bases for my cushions that fit the contour of the boat, and just staple the vinyl to the bottom. Very simple.

A cheap source of foam is free sleeper sofas on Craigslist.