Your 340crs will do just fine for VHF airband monitoring!
I'd dedicate a bank just to airband, and not put it in with the others. Airband communications can be frequent, but short in length, so if you are scanning 50 channels or more at one shot, you could miss some comms. Note that in your area, the fields are mostly un-towered using ctaf/unicom frequencies rather than dedicated tower freqs. You may also not hear them when on the ground.
Your best bet is to go to:
AirNav: KUNU - Dodge County Airport
Look for the Unicom/CTAF frequencies. Also look for the Approach / Departure frequencies. At the bottom of the page, you'll see other nearby airports. Go to them and plug in those ctaf/unicom and other approach/departures. KUNU's ctaf/unicom is 122.700. Watertown's is 122.800 but there are more!
This should give you a good start. Plug in the unofficial 123.450 air-air freq.
You've got a very nice selection of local municipal airports to listen to AND to visit! Seems like KUNU was a great stopping point for those going to Oshkosh...
I also notice that you have a few private landing strips without any listed freqs - so you may want to search or inquire as to what those freqs are later on...