Traveling from NC to PA next week and need lodging advice?

I am gonna be traveling up I-81 to a big Christian Music Festival in PA next week and my plan was to leave home here in NC on Monday and get a hotel room somewhere around the PA State line about 2 hours from my destination and then get up early Tuesday morning so that I can be there when the Creation Fest gates open @noon but I’m a little tight on funds and can’t seem to find a room for less than $50 on any of the discount travel sites. I have a quick set pop-up tent so I was pondering the ideal of maybe finding a spot somewhere on my route, pitch that thing up and catch a few hours sleep ,then finish my drive out Tuesday morning (btw..it’s an 8 hour drive from where I live in NC to PA). The questions is, Can I “Legally” do this? Does anybody have any advice on a free or very reseaonable way to just catch a few hours sleep other than sleeping in my car (there won’t be room in my car to sleep)? Can I perhaps pop a tent up at a rest area along the way? I’m open to all suggestions as long as it’s legal cause I don’t wanna get arrested. Thanks & God Bless.