Very nice trailer and some good information. I don't have near as many restrictions to deal with as you do. Like height limits and brakes. So I have a more flexibility.

I like the box shape as opposed to the tree, I see advantages but I wonder about loading the boats. Since my boats are SOF I just pick mine up and place them on the tree. Having to slide them in looks like a lot more trouble. When I haul some of my buddies plastic boats they are very heavy and that really seems like it would be harder to load.

Then you have to have space behind the trailer to slide them out. Not usually a problem but some of the spots I go that could be an issue. At some of the ramps I could find myself sliding the boat out and standing in traffic. One of things I really like it how easy it would be to put a tarp side on that frame and enclose the boats. Keeping them out of sight.