RobA, I'm searching for an answer on this same thing and came across your post. What did you end up doing and how did it turn out? I am actually building my dock on the ice since it should be around summer water level and reasonably flat enough to just put down some spacer blocks that I will set my headers on. I am also building with 2x10 headers and dock framing. I am most concerned with getting the finished deck elevation to be close to the deck of my pontoon (though I failed to measure that exact height in summer). When I looked up pontoon deck height online I see a variation from 13" to about 18". Considering that just my 2x10 headers plus my 2x10 framing plus my 2x4 decking will take up 20" plus any distance I shim the headers up, I am probably looking at about 24" above water line which would be as much as 11" above my pontoon deck.
