I am about to buy a Fishfinder for a 15" John Boat.  I wasn't sure what my options were for mounting.  I've seen those mounts that they have at Cabelas, but I want something a little more permanent.  Is there a website out there that gives you a little more direction for installation?  

Go to the Lowrance website and download a manual for any sonar unit. Just scroll through the pages until you get to the installation instructions-somewhere in the first part of the manual.

For mounting hardware.. go to ram mounts.  They are awesome.

Ok this is how I did it on my Jon boat; transom mount the transducer as per the manufactures instructions. Install the graph on the front deck and then go the menu page to see how to increase the font size so the screen can be read from the rear set as well as the front while fishing.

If you don't want to drill holes below the water line, you can install a board like the ones provided with Lund boats.  You put the td on the board and attach the board to the transom above the water line.

I use a suction cup mount and it works fine.  You can also mount the transducer on a long piece of wood and then clamp the wood to your boat when you want to use the fish finder.

My buddy mounted his transducer the way jigman suggested, and it worked out well.  That was the same way my dad did it back in the day when he had a boat.

I mounted my transducer bracket by drilling the holes for the screws... once the bracket was attached, I used Marine silicone and sealed everything...absolutely no leaks.  I then ran the wire up an over the transom, using a wire tie to the handle? on the back of the boat. then to the front to the unit.

i have not personally used this method but there r mounts available that attach to the end of your trolling motor>  simply attach run the wires up  to the graph   and attach that anywhere.  no need for any holes.