Re: Adding a auxiliary outboard.
Make sure you use a mount that is spring loaded to assist with the motors weight and has enough travel to get deep in the water.
How thick is your transom? I'd think a 1in backing plate would suffice. We mounted one on our boat, but the transom on ours is 1/2in thick. We used a 3/4in starboard backing plate and washers, it has held up fine.