I've done exactly as SabreKai mentioned with great results. I first did it as a rush job prior to heading down the ICW
. It was meant to be temporary but when it worked so well I ripped it out and reset everything more permanently. I used a PVC clean out fitting and mounted the transducer in the cap. I space it down from the cap a little into the fitting (which became the well) so if there is any air trapped inside, the bubble would always be above the transducer head at any angle of heal. Next time the boat is hauled I plan to remove the old non-working head and fill the hole.
I used vegetable oil but I've heard vasoline works. If that's true, it would be great because it would never leak. Of course, with careful installation and sealing of the well it won't leak either.
As far as recommending a unit, I used a Garmin
through-hull transducer. I spoke with Garmin
about using their unit in the way I planned and they said it *should* work if the hull thickness is less than 5/8". Keep in mind the curve of the hull adds thickness if the transducer is aiming straight down.
Best of luck!