I have a suction cup attachment, but have seen individuals with the transducer set inside the boat. Thoughts?

I've used mine through the kevlar hull. Works fine. Make sure you are not trying to shoot through the foam in the middle. It helps to have a little water under the transducer.

I have an ice fishign unit. I set the transducer right on the kevlar hull of my Souris River canoe. I do have to splash a couple drops of water on the bottom to get it to read.

Get a pool noodle (closed cell foam), cut about 1 1/2 inch off. Take that portion you cut off and trace the profile of the bottom of your transducer in the center of the foam. Take a fillet knife and cut the profile out of the center of the foam. Make sure the transducer fits into the cutout (I like it to fit snug). Silicone the foam cutout into the bottom of the canoe where you want the transducer. It only takes enough silicone to make a watertight seal. Just place a small amount of water in the foam cutout and then push the transducer in and the excess water will push out. The transducer stays put and is easily removed for travel, portaging or using in another boat.