I use a Bottom line Fishin' Buddy and love it. It is a side scan and down type and the side scan is a wonder. It also has the temperature and such. Since it is a self contained unit with screen,batteries and transducer all together all you have to do is figure out a way to mount it. I have a PVC frame I built for my tube so it is no problem.

The thing about side scan is that you don't go over the fish that you are seeing and so they are not spooked. I actually seek and catch schooling bass and white bass with it and have tremendous success spotting the fish.

Thanks Dan, after all the advice, I will be asking my wife for a fish finder for Christmas.

My fish finder works great, for about 8 hours, on the small Dewalt 14.4 cordless portable tool (drill) battery.

Also, on my Kennebec, which has two long straight tubes
I put in large pieces of 1/16" polypropelene secured with rivets, the shield the tops of the bladders against punctures, from hooks in the storage bags.
The added regidity helps prop up the strap on depth finder.

went to sportsman's warehouse going out of business sale today. bought a bottom line fishin buddy 2202 for 80.00. it sales for 150.00 at bps. they still had about 5 or 6, I even saw a portable that you wear like a wrist watch for 60.00. most items are 40% off now.

That wrist unit is a Hummingbird, and it is a piece of junk--resolution looks like an old Atari game. You'd be getting a bad deal at $10.