In my opinion if you have a transom then that is the best place to put the transducer. The less movement the less problems you will have to troubleshoot on the water and you always know where it is located to throw a marker out.
I like to have my TM able to move on spot lock and not change any views of the ducer. Also if you want to add a Livescope later you can make a simple over the side mount to be able to rotate it by hand to see in the water.
I have a jon boat and mounted my ducer on the transom. On my kayak I have it in the middle in a retractable plate to protect when moving or beaching. I use my Livescope on an arm I put down when I am ready to use it. I have the 74SV.