Advice on mounting / rigging fish finder older style xfactor

[Irishman]

I have the older style xfactor, no transducer thingy in the hull. For Christmas got the lowrance elite 4hdsi (non gps)
My questions to those who have walked the path before me...
- where did you mount the actual head unit and where did you wish you had mounted it once fishing and ergonomics came into play
- location for transducer? Over the side or in the hull?
- any tips would be much appreciated, am looking to pay the guys at OEX to do this right for me the first time round.
Cheers and Happy Christmas