I was just thinking...........I know it's a little ways to the southeast of Oshkosh (just over an hour drive each way:
http://maps.google.com/maps?hl=en&tab=wl). But Elkhart Lake, WI is a really cool town to stay in.
Airport info:
http://airnav.com/airport/KSBM or
http://airnav.com/airport/8D1. I'm not sure about rental car/courtesy car availability.
The two hotels that I know of:
The Ostoff Resort
http://www.osthoff.com/Siebkens Resort
http://www.siebkens.com/. Siebkens has great food and a great bar next door.
More hotels in Plymouth.
Two more great places to eat in Elkhart Lake:
The Paddock Club
http://www.paddockclubelkhartlake.com/. The Hangar Steak is the bomb here!!
Lake Street Cafe
http://www.lakestreetcafe.com/.
Another bar with great food (one of the best burgers I've ever had). The Brown Baer at 181 East Rhine Street Elkhart Lake, WI (920) 876-3319
Again, I know it's out of the way for most, but it may be well worth it to some.