I put the transducer depth finder in my 1997 Challenger, without a hitch. It was designed to be put inside the hull. It shot a signal through the fiberglass.
Not much info there.. how about attaching what type of depth finder you have. That would be a big help. Even attaching a couple pix. I'm on nightshift for one more night. Get it up by tomorrow evening, I may can get you in the right direction.