This seems fairly typical of what I was referring to.
riverboat.jpg
A Google image search will turn up dozens more.
As for warping the deck... I can't think of any tricks. You may have to build a new deck.
However, looking at the Google Images... about half of them only have a 'slight' warped effect.
Many are also flat save a short bow or aft section.
Give the pics a look.
You do not have the required permissions to view the files attached to this post.