On my inflatable I also have a fishfinder. More or less the in way you describe it.
I have just one bench in the Zodiac, so I am sitting on the tube, in front of me on the bench is the fish finder and a compass, keeping one seating place open (for the ole ball and chain...).
The battery is mounted in a box under the seat, so that I don't have too many wires running back and forth. It is a small dry battery of just 4AH, plenty to make a full day on the boat or several shorter trips.
The transducer is transom mounted...took a bit of experimenting on the position (out of reach of the propellor
and not disturbed too much by air bubbles) not so easy on such a small transom.
At the end of the day I just take the whole seat of and take it home (I leave the boat on the trailer at a farmer near the slipway).
There is just one downside on the whole thing, when we are diving we have to be very carefull not to knock the FF of the bench while trying to put fins on or moving around the boat.
But it is a great instrument to have, you can't do without when diving but otherwise it also gives loads of usefull info, ask Graeme!
I would say Go for it...I have even been thinking about a GPS...but now with the plans for the new RIB in 2003 I leave it for what is is...
Eddy (who eats fish every day now) Veuger