Hawk, I don't know that any reinforcement needs to be anything exotic or even complicated. I'm a great believer in always trying the simple solution first and the majority of times it works. If I were sitting in your shoes, I think I might just take one of my trusty popsicle sticks, cut it to fit and goo it up with a bit of fast epoxy.......then slap this on under the deck. That should stiffen up the deck and spread the load.

Also you can tune out a bunch of that weather helm by pulling the mast forward rather than to the rear. Most people think the more rearward their mast is pulled, the better. Play with some tuning.