GPS/Fishfinder Options for '14 200

[MoRiver]

I have a 2014 Cobalt 200. It has the little LCD thing built into the Speedometer that you are all familiar with. Love my Cobalt so far, but I want a more substantial depth finder & plotter. I don't want to drill a bunch of holes either!

My previous boat, I just glued an in-hull transponder in the bilge and mounted the main unit near the dash. Pretty simple and it worked. I mostly boat the Missouri River. It runs about 20' in the channel and can ramp up quicky to shallow depth that i want to see on a screen as I boat to the sandbars.

I know a Cobalt has a thicker hull and there's already a factory transducer in the bilge. Can I tap that existing unit? Do I intsall a new transponder? Recommendations?