The trailer needs to hold up the transom if your motor is hanging on it. In a standard sib I have had flat bunks 2'X10" with carpet under the tubes that can catch the outside edges of the transom & outboard weight as well. My Futura now has two 2x4 boards on edge with carpet just inside the speed tubes. They are extended enough to hold the transom as well.
Don't make your transom hang in the air with the weight of the outboard hanging on it all the time. Just my thoughts.
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