If you plan to epoxy to the hull the Lowrance owners manual provides good instructions--- at least for the LCX models. The manuals are available on line. If doing an oil bath cannister setup, the intallation instructions for the Airmar m260 are very detailed--- also available on line.
Follow the instructions in the manual if you can get a cylinderical piece of something and fill with light weight mineral oil during a test drive. 2-liter bottles cut in sections will work if you have a smooth section of hull and drop a rock or weight onto the transducer and fill with oil for a test run. I don't of any newer transducers that won't shoot through a hull epoxyed in place - the key is working the transducer into the epoxy to remove all air bubbles.
You could also clean the hull well with acetone or mineral spirits and use Lexel to attach the transducer to the hull. Using Lexel you can remove it. Using epoxy you will destroy it trying to remove it.
I used Lexel in my kayak and it is some tough stuff. Just takes a while to cure, but when done, no pounding is going to loosen it up.