Personally, I think that 12+ ducks is just too many ducks for a tractor style coop. Ducks are so messy, I just think that a tractor isn't a good match. Maybe someone here has made it work and can explain how they did it. I agree, chicken wire is inappropriate for flooring for several reasons, #1 being it just would not likely be strong enough to support ducks' weight, and #2 it alone doesn't really offer any real predator protection. Finally #3, my bet is that ducks' feet would suffer damage/injury from that.
I think that Storey's Guide explains housing requirements this way: first, you as the owner decide how often your ducks will be confined: 24hours per day? Those ducks will need the greatest amount of space, I think the rule is up to 7-8sq ft per duck. Ducks that free range for half the day and are only confined at night, I think the housing square footage can drop to as low as 3 square foot per duck, depending on breed, size, and dynamics.
Based on those numbers, my opinion is that the structure you would need would simply be too large to be a tractor.
ETA: for my outdoor pen, I have 12'x24' for my ducks, so 288 square feet. Divide that by 12 (for each duck) and you get 24 square feet for each. I personally would absolutely not go any smaller.
