Hey Willy, Maybe you can find a round baitwell that'll fit in the opening of the floor, than mak a filler piece for the deck.
http://www.basspro.com/servlet/catal...=SearchResults
http://www.catchnbait.com/livebaitwells.html
That way it could be pretty big, only there whem you need it and taller too so you would not have to crawl all over the deck