If I were adding a pre-made SWP I'd almost certainly get it from Swimplatforms.com. I talked with the company reps at a sporting goods show in Phoenix a couple of years ago then toured their plant in south Phoenix.
You nailed it, they have been really nice to deal with and I plan to order from them.
I have seen pics of your swim platform. It's bigger than the cockpit of my boat... We plan to buy a live aboard boat, with living space in the size range of yours, in the next few years, but we have no plans to get rid of our current boat. We love it too much, thus I have no qualms about spending money to upgrade it.