I have done KOXI Starke County and KANQ Steuben County both are about a 2 hour flight to OSH. Both have reasonably priced self serve 100LL. Steuben has a very nice 4,500 ft runway, but no OSH vibe. I was the only one there, but the weather was not the best. It does set you up well to go north up Michigan and then across the lake. Stark did have an OSH vibe. Free hotdogs and donuts along with a few other pilots making the trek, but on that visit the flying weather was about as good as it can get.
Portage Muni C47 is only a few miles south of the Endeavor Bridge. I stopped there when I showed up late and the air show was starting and could not get into OSH. Great hospitality, but there are no taxiways, so it could be a mess if there were a lot of traffic along with having to back taxi on the active runway. But, the location is perfect for getting into the conga line.