David,
When I was asking your question in my search for a trailer it became apparent that the dimensions are not as straight fwd as one might think. The bunks and the way they distribute the weight of the boat became like a college math/engineering test. If they don't kiss the boats big curvaceous bottom just right, and perfectly line up with the boats strong points and the trailers sweet spot then you end up with a bruised hussy that hates to be handled.
I found a stout powerboat trailer and fabricated a fantastic hauler but it takes time, tools and experience. I'll measure a few points on mine to give you a head start. Here's a diagram I found useful when building mine. Cya, Mike