I have a new Garmin 160c to mount on the cat boat .Anyone have any suggestions on the best way to set it up?

Didn't it come with a manual?  if not you probably can download one off of Garmins website.,,,the Transducer should be placed as far a way from the motor as practical----get a plastic cutting board from wall mart and cut it into a rectangular shape,,,then with sheet metal screws attach that to the transom---remove and seal with a sealant.....this will allow you to repostion the transducer several times if it is to low or two high without adding uneccessary holes in the boat.  Never trailer the boat with the screen mounted---especially in rain --- its water proof but not at 60 mph...Never leave the unit on with the transducer out of the water...that use to heat them up and destroy them,,but I think they have improved in that area 

Most people put em where you can view em while "driving" along,,,I cant remember whether you have a tiller steer on steering wheel---for the tiller steer maybe on the left side of a bench seat so you can face it while manuevring along