It will work inside but do not mount in on the step. The step on my charger, when I am up on plane is out of the water. When they put the flasher in they mounted on the step it didnt work but has been moved to the bottom of the boat. On other choice for mounting on the outside try this from cabelas. The guys over on walleyecentral sure seam to like them alot. Aslo make sure your existing transducers are not running on the same freq. in the back of the boat. The cones will overlap each other and cause problems.
http://www.cabelas.com/cabelas/en/te...276&hasJS=true