I prefer the Allstays app. I do not travel with reservations - just against my principles - unless I need to be somewhere for a specific reason, like a wedding or visiting kids. The only time that is tricky is if it is a holiday and a Fri and Sat night of the New Years Eve holiday would certainly qualify. Instead of looking to stay in a destination type campground on a holiday like that - a KOA, Stone Mtn, RV Resort, a place that plans holiday parties etc., pull in for the night without reservations even at a travel type campground - like one that caters to the interstate traveling public.
If you are just "nervous" about staying at Walmarts because of all the traffic and possible "undesirables" but not against the concept of boondocking for an overnighter, consider instead Cracker Barrel. With very very few exceptions, they welcome RV and have RV parking spots. I stop early when traveling so I usually pull in @ 2-3 pm and use an RV spot. Eat supper there and then around 8ish, when the lot starts emptying, I pull to a curb across a few car spots and put my slides our across the curb/grass. For overnight, I avoid an area where the trash truck will pull in early morning and avoid the curbing area which is near the entry and will fill up with breakfast patrons. Good, lighted, quiet, police patrolled but not bothersome, parking spots. When eating dinner, I ask for the mgr and make sure its OK to stay and sleep 'awhile'. It always is. Pick up a CB location map at any of their restaurants.
Another place I like to stop overnight at is suburban/rural (non parking ramp) hospitals. Security is almost always at the ER entrance. Stop in the evening and ask security if there is a corner of the parking lot they would recommend for a tired traveler to get a few winks. Generally, they will get in a security car or golf cart and escort you to a good spot. Very quiet at night, well lit and patrolled. Hospital cafeterias aren't bad for breakfast either.
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