Can I get some help on building a mobile wifi hotspot?

So, I've been wanting to turn my Jeep into a mobile wifi hotspot that works when I go offroading out in the hill country. I was thinking about using a parabolic grid antenna to access unlocked wifi and then hooking that up to a wifi repeater to create my own free wifi hotspot. Unfortunately, I don't have the slightest idea of how to do this. Help? What would I need? Is this even possible?