Not many people know of this scam, here is what you do.
Park in the hotel complex parking lot 1/2 mile south of MDW and walk into the hotel, there are 5 of them. Ask for a shuttle, (free of'course), and they will take you to the gate. I do it every month and park for free leaving my car/truck for weeks at a time. As far as they know, you are staying there, they don't really care, I asked.
I used to parked across the street at the 36 tiedown until they built the tower there and ruined it for everybody, so with a little improvising, I figured out a way not to give that dick Daily any of my money. I leave with a big smile on my face evey time I get over on the city. If you have any detailed questions regarding this technique, just PM me.