Mounting the transducer on the TM is done all the time on bass boats and such, without ill effects IF you mount it correctly, and power the FF from the cranking battery and NOT the battery used to power the trolling motor. BPS or Cabelas have the mounting bracket, and if you buy the FF new, it may include the bracket and worm clamp needed to mount it properly on the lower motor portion of the TM.
Check out youtube, and you'll find several vids on how to mount one. I've had a FF transducer mounted on my TM for years w/o issue, just don't power the FF with the same battery for the TM. May have to do a bit of fine tuning/adjustment on the transducer to get a good picture on the head unit, but actually its easier to do than learning how to use a fly rod imo.