Dave, the Elite 7 comes with an HDI transducer which is meant to mount on the outside of the hull. That's what is so unique about the Elite series is they already have downscan capabilities built-in in addition to the traditional 2d sonar.
You could shoot it thru the hull, of course, but that would be a waste of a good transducer.
YOu could mount the HDI transducer on your TM and buy a shoot thru ducer to epoxy in the hull and buy a switch box that the 2 transducers would plug into. That way if you mounted the elite head unit on a ram mount you could spin it around while fishing up front and switch it to the TM ducer and fish. Or better yet, mount it up front on a ram so you can see it from the drivers seat for mapping and depth while you're driving.