I have a rollercoaster trailer too and have the same problem with the rear ratchet straps. The problem is that the trailer frame doesn't protrude out below the transom. The hull does bounce on the rollers when it goes over a bump as the straps are not vertical. I'm not really sure what the answer is. Roller coaster are brilliant trailer but this problem is a trade off.
However, I think that the near horizontal angle of your rear strap will allow the boat to lift at the rear on bumpy roads (i.e. you somehow need a more vertical pull down on the stern to trailer connection).[/QUOTE]