You are a prime candidate for the jackplate mounted SI transducer utilizing the Transducer Shield and Saver with the custom L bracket designed for your jackplate. No holes in the hull needed.
That system positions the large expensive transducer above the hull bottom for protection and allows for SI use at idle speeds.
The SI transducer has to be externally mounted to function with SI.
Very few ,if any, performamce bass boats have any success with a transom mounted transducer for on-plane depth reading. You have that covered with what you have now.
A phone call to that company with a description of your boat and setup will get you a top notch rigging.
There are many dozens of transducer installation pictures on Bass Boat Central Humminbird forums and the Side Imaging Group on Yahoo for reference.