HB HELIX12 Sonar GPS. You wouldnt need a G2N since you wont be networking it to another unit , so a Gen1 would save you quite a bit of money.
I believe (not sure on Gen1 units) they have 2 map card slots. 1 LakeMaster card & 1 Navionics card would do the job.
I agree with going with the Helix 12, unless you just want touch screen, but for just mapping I am not sure that the cost difference between the Solix and the Helix would be worth it.