The RV you choose MUST be self-contained. If you want to camp free, this is an ABSOLUTE NECESSITY. And the stuff has to work. And make sure it doesn't leak. If you have a trusted mechanic, have him inspect it for you -- it will be money well-spent. If you don't know one, FIND ONE.
There is a pretty good book that I have right now from the library on an InterLibrary Loan (ILL): Camping America's Guide to Free and Low-Cost Campgrounds. This one is the 15th edition/2014. It is for sale at Amazon for $15 ($22 in bookstores). Each state has a map, plus listed by nearest town. The prices range from free to $12/day. A Senior Federal Pass will save you half the cost at many of them. It also tells you if overnight parking is allowed in the state rest areas in that state.
Each entry gives info on:
* Directions to the campground
* Price, and variations
* What part of the year they're open (many open all year, dates can fluctuate esp in high-elevation and extreme weather areas)
* Number of days you can stay (most are 14 days)
* How many sites and what length limitation
* Elevation if it affects availability
* Facilities available (or not): tables, toilets (pit/vault/flush), showers, picnic shelters, campfire/grill, drinking water, bear boxes, electric, sewage dump, laundry, etc.
* Interesting stuff: boating, canoeing, swimming, beach, fishing, hunting (in season), hiking, rockhounding, interpretive programs, guided hikes, nature trails, scenic overlooks, cafe, store, historical interest, etc.
PRIMITIVE can range from just a campsite (nothing else) to a campsite with table, fire ring, drinking water, vault toilet.
It also tells you which states allow overnight parking in state rest areas (one night only). Those states happen to be AK (unless otherwise posted), AZ, AR, CT (emergencies only), DE (allowed but not encouraged), IL (only on IL Toll Road- no facilities), IN (only on IN Toll Road- no facilities), KS, NV (unless otherwise posted), NM, NY (emergencies only), OH (only on OH Turnpike), OK, OR (14-hour limit), TX, VA, WY (some limitations). If there are variations, they should be posted.