As a single woman, I stay at Walmarts, Flying J, and Pilot and have always felt safe. Stay only at the 24-hour Walmarts and park under a light as previously suggested. Ask at customer service if it is ok as some towns have ordinances against this or that particular Walmart may not allow overnight parking. I get my supplies and food before dark and stay inside for the night. As an added note, I try to park where I can get out quickly without getting blocked in.
Got blocked in once at Flying J by a 5th wheel who came in after dark and had no consideration for others. I wanted to leave by 7 am and he was still in bed.
