I've never called ahead though I suppose one could, especially if you want a hangar (but why worry about that if you're going to spend a week tied down outside at OSH?). If nobody's around and there are no spots labeled "transient", just look for a spot with no ropes in the rings or old faded ones (so it's not a spot assigned to somebody who happens to be away), and use your own ropes. Landing fees at small airports are rare, some charge overnight, some don't. If you plan to camp overnight, the smaller the airport the better, grass fields even better. I also look for airports with restaurants within walking distance if I'm staying overnight. My MO is to look for grass fields along the way first, then paved if no grass, and use google earth to see what's around the airport. And be flexible... it sounds like a long day of flying, you may well want to stop much earlier.
Also, don't pitch your tent underneath the airport beacon. They can squeak once per revolution...all night long.
If airport has a Medevac helicopter based there, prepare for the sound of turbines kicking in at 2 in the morning. (Which was actually pretty cool. Sounds like alien spacecraft coming in)