One of the best ways of mounting your transducer to your SIB is using the Railblaza transducer arms with either a Quickport or a RIBPort. 
 
If you have the Honwave style extended floor tabs then choose the longer arm. 
 
If you don't have the extended floor tabs then go fo the shorter arm. 
 
You then mount the arm on to a Quickport that can be screwed or glued to your transom. 

If your prop rotates clockwise, to avoid the wash interfering with reception, position the Quickport to the right of the engine (starboard). 
If your prop rotates anti clockwise then position to the left (port side)