I have two ducers set upon a factory bracket on the back of the pontoon, takes a little playing with to get em adjusted and they don't work that well high speeds but they work super good when fishing.
I have two in case one fails which happend a few times several years ago.
If thee is room with the boick up for your live well, put it there, or have a bracket made and have it welded on the other pontoon. There is another bracket made I'll send you the web site, clamps on the back of the boat and hangs down behind the pontoon. I use it but had to have mine modified some but the company is real good and will make anything you need.
E mail me in private and I'll send you the web site.
I also have my transducer mounted to the bracket on the back of my pontoon. My port side has the pump for the livewell on it and the starboard has the transducer on it. I used it all last year with absolutely no problems. I have to agree with John though, mine doesn't work well at high speed either but is perfect at trolling speed up to about 10 mph. I think the water turbulance(??) coming off the back of the 'toon that screws it up.