Thru-hull Kayak Chart-plotter/GPS?

Hi,

I fish out of a Native Slayer 10 and am looking for some advice on what I should be looking at in a sonar unit.  My main interest is in seeing bottom contour and the ability to make my own maps/charts.  I care less about trying to spot fish then just getting a clear idea of what the bottom looks like.  I fish a lot of spots with poor to non-existent charts and mainly just want to get a basic idea of what the bottom looks like.  I want a unit where I can mount the transducer inside the hull and keep the unit and battery in a Cellblok or something like that.  I don't mind drilling a few holes or chasing wires and the ideal is something where I have the fastest/easiest set up and removal of the unit/battery.   

I am not sure what terms to even search for as sonars/fish finders seem to exist in a ocean of acronyms, so my googling around has been less then fruitful.  I would love any advice or ***.

Thanks