Those flying in for a day trip, Basler offers hard surface parking but you must make a reservation. Just give them a call at 920-236-7827 and make a reservation for the day. Easy in / Easy out.
The other option is Fond du Lac, KFLD. Great little airport but must have an IFR reservation to get in by Instruments. VFR no problem just give the KFLD temporary tower a heads up at least 10 miles out on 120.4. Using KFLD gives the option to leave anytime in the evening. No restrictions departing KFLD after the airshow. Night arrivals are discouraged but departures are ok. Be careful departing as there is camping on the KFLD airport runway 9-27.
There is a shuttle bus that runs every hour to OSH that is $15 one way or $25 round trip. Starts operating about 0700 til 2200. The last bus leaves OSH at 2230 for KFLD.
http://www.fdl.net/eaa572/page3.htm
Hope to see ya there SOAP'ers