As I recall, my buddy mounted the transducer on a piece of 1x4 board, then used a c clamp to attach it off the transom. He has a willie drifter. Worked fine, I did the same on my old non-db too. Just keep the c clamp away from your anchor line. If you want to make it more permanent and less snaggy on your anchor rope, you could attach the board to the boat with bolts (above the waterline), but then you're drilling through the boat and that may or may not be your style.
Best,