You can buy trolling motor transducer mounts right here on iBoats. It is a clamp arrangement and they work just as well on the troller as they do anywhere else on the boat. If you happen to have a MinnKota Power Drive motor, there are some cable routing tricks you need to know about and I can provide pictures of how that process works. If you have a sissor type mount then you simply zip tie the transducer cable to the motor shaft. It is not in the way.
That works fine, unless you have a troller such as a MinnKota Power Drive or similar. If the motor shaft needs to slide through the mount while being stowed or deployed, you can't tie the cable to the shaft.