Don't rule out tuff coat. I looked at all of them including duraback. The reviews on tuff coat were to good to overlook. We did a 18/60 aluminum a few months ago (inside and out) and so far it's wonderful. Here are a few things I can say about product.
1)use their primer
2) check colors to be sure they match what label says before you start. I repeat ... check the colors!!!
3) buy a cheap texture sprayer and practice on cardboard first . Once you get the air pressure correct , a monkey can spray it on . The few areas I had to roll/brush due to the large space needed to operate sprayer, did not turn out as good.
4) it is a ruffer texture than rhino, which is what I wanted , but the only rhino dealer ( who could color match) within 200 miles of me stood me up on TWO appointments, so he got a pink slip.
5) if you slip down with tuffcoat on your deck... you probably don't need to be on a boat.