[flyingfrizzle]

What are you considering risers? The stingers? if so they should be solid fiberglass with foam in them if that is the case. No wood to rot there. Far as the deck 1/2 marine ply like douglass fir or such would be a good wood choice. Aquatech is popular as well. You need to make sure you get the fiberglass lay up right due to most of the strength comes from it and not the ply wood. The wood is just a core and adds some strength but the true strength comes from the glass lay up on both sides of it. Far as raising it up, parrot's 2x4 idea works well and many others just raise the box stringers up whatever height the want. The project boat I started this weekend had sections cut out of my stringer tops to refill with pourable foam so I will just raise mine cause the stringers need new tops any way. If yours are in good shape I would just add to the top of them with stacked 3/4 marine wood strips layers to you get the height you want or the 2by idea would work well too. You might want to check to make sure your foam in the stringers is dry first cause if it is wet you will have to cut the tops to get it out any how and that might determine the best way to rebuild them higher.