I did this in 2 mm ply. I dampened both sides of the ply, then taped and clamped it over the formers, with a little extra packing to allow for the double curve easing after I had finished. Then I used a hair dryer on the wood, not rushing it. Half an hour later, job done.
I also built a decent coaming, around the sub deck, shaped to fit, so that I had a generous surface to glue to. It probably worked because the curves weren't too extreme, so it depends on just how much curve you've got to put in..
Chas