I am getting an education on this topic with the help of you guys and some others as far as using treated wood for this project... To answer peters question, yes the cross beams the floor fastens to is aluminum... I actually never knew there was a dis-similar metal issue involved with the treated wood... I have taken the old flooring out and there doesn't seem to be any problem with the structure underneath... Now I'm concerned with the bolts and washers that have to be used to bolt the floor to the cross members... I am planning on using stainless steel elevator bolts and nuts but was going to use standard plated washers from the local hardware store, the washers and bolts that were on the thing were rusted solid but there wasn't any damage to the aluminum... Should I be concerned about this or is that just a monster in my mind?... Both me and the pontoon have had several birthdays so another 15 or 20 years would be about the outer limits of how long this project needs to last.