Thru Hull Down Scan does work but there is a little bit of loss from what you are scanning.
When mounting the ducer inside the kayak I have tested all the installations and the only one I will ever use it the electrical putty installation. It never dries out, the readings are very good, and your transducer will not come loose unless you pull it loose.
It's clean and not permanent.
Below is an image of a thrull hull installation. Side scanning doesn't work too well but Down Scanning works well enough. However all that being said, if you can mount it in the water I would recommend that more than anything.
