I have a Northtrail trailer, It has a straight frame, my bunks are set at 17 3/4 inch at the top inside edge of the 2x4, both front and rear are the same, the bottom inside edge of the bunk to the top of the frame measures 4 3/4 inch, that gives me about 3 inches from the bottom of the seadoo to top of the frame, I need that much height because the winch post goes under the seadoo and I end up with about an inch of clearance.
I ordered a spark trailer but it ended up being too wide for my garage door, first brochure I read said it was 2.5 but it ended up being 2.6 so I kept my old trailer, all I had to change was I moved both outside bunks in one hole and they sit perfect!