Gben,
I have a floral city airboat with twin lenco trolling motors. If you are going to mount your motor on an airboat you will definitely want twin motors. A single motor (no matter where you mount it) if it gets windy, with all the wind resistance an airboat has, you will basically just go in circles without a lot of control. All of my friends have singles both mounted front and rear and they hate them. Singles are great on our flats boats but not well on the blow boats. With the twins you can operate them just like twin outboards with forward and reverse. They give you complete control over the boat in any weather condition.
Mark