Hello Gary....
This is the FB page for a local dock builder who has been building them here for quite a few years.
Might be worth reaching out to him for his opinion (?)
If you go down to the May 17 video ("Just completed") - I actually watched the construction of this one as it is across the street from one of my accounts. And it has a flat second story deck.
He uses a product called "Weardeck" apparently.
My client's dock is also seen in the video (they have a pontoon boat) and it also has a flat upper deck.
https://www.facebook.com/NSBdockguy/
I think the owner's name is Brian. I met him a few years ago.
There are other dock builders here - one I've known as a friend for probably going on 50 years.
Good luck! And let me know if I can help with anything else.