Hey Paul:
Welcome to the board. Do you already have the trolling motor or are you going to purchase one? They make TMs expecially for mounting to the front of pontoon boats. The brackets are designed to mount to the deck and have a quick release so the whole TM can be removed when not in use and for storage/security.
http://www.minnkotamotors.com/produc...nt/pontoon.asp
I've always had problems in the past with TM mounted transducers - sooner or later the transducer cable gets damaged and the transducer has to be replaced.
TighLock makes a memovable/clamp on transducer mount that may work for you.
http://www.amazon.com/exec/obidos/tg...89769?v=glance