Staying in a Walmart lot isn't always about just saving money. I've actually only done it once myself and that was on a cross-country trip from California to Wisconsin and back. I did a Walmart one night but did Cabellas, Cracker Barrel and several nights of just parking on the street in a business area. The main reason being it was just easy to pull off the freeway and park and go to bed and then get up in 8 hours and get back on the road. There was no need for water or charging the batteries. Just a need to get some sleep and head out. No reason to try and find a campground and get checked in and pay $20 to $50 just to get 8 hours sleep.