I have been using a similar set up for a while. I have the Vex FL-18 that has bottom lock. I have the round "trolling motor" mount transducer. I didn't like it on the motor so I rigged it to a bracket I purchased through Cabela's. You could rig something similar (I did several years ago) using black electrical tape and a SS hose clamp. Wrap the tape around the transducer (to protect it) and hose clamp the transducer to a mount.
The only problem you may have is going at higher speeds. I was using a 36 lb thrust trolling motor so I was moving relatively slow. The water hitting the round transducer causes a "wash" and accumulating bubbles. This can give you all kinds of false readings. If I have time later I'll post a picture of my set up. :wink: