sorry for the late reply, but, what unit are you running on the stern. I'm trying to determine what unit would be best for me. I am wanting to do about the same thing you are describing. use the unit with side imaging to locate brush piles and or bridge pillars that have brush/fish around them.
There are so many type nowadays its really difficult to pinpoint what would work best. I'd like to have the side imaging, gps and of course down imaging.