I recently bought a new to me fish finder a lowrance HD5 , but been trying to research where and how to put the transducer mount on the boat . So my question is should I go with putting it inside the hull for the sake of not drilling holes in the boat ? all information gratley appreciated. Boat is a triton TR20 2001

You unit should have installation procedure included. This seems to be a common question and this site has lots of lists related to "how to mount a transducer".

If this is your console unit epoxy the TD in the sump drain is a common location, remember this will eliminate the temperature reading, the sensor is located on the bottom of the TD. 

Tom