I went last year as well and did the USAF museum in Dayton as well which was fantastic and well worth the visit. Getting from Dayton to Milwaukee wasn't easy, ended up going via Baltimore on AirTran/Southwest, was a bit of work but not expensive.
Great roads and it's not far to get from MKE to Oshkosh, we left earlyish the last day and drove back to MKE and stayed at an airport hotel which was really nice and cheap. Really lovely people in MKE/Oshkosh area, as well as Dayton, they couldn't imagine why an Australian would be there!