If you already have the Disability Access Pass then use this site to find campgrounds along your way:
http://www.recreation.gov/The pass can be used for free general entry for all the major national parks such as Great Smokey Mtn., Yellowstone, etc.
It can also be used for 1/2 off on camp fees. If a site has electric then you will get 1/2 off on the camp sites plus a nominal charge for electric. The campsites will usually cost you from approx. $8-$15/night.
Not all campsites have electric so you're going to have to do your research on this. However, if you're just spending a night or two in an area and the temperature is cool (mountains or coastal regions), then you can probably do without electric.
The pass can be used at national parks, national monuments, Corp of Engineer parks, BLM campgrounds, Fish and Wildlife and national forest campgrounds.
We have never found a concessionier-run campground that didn't honor it, including Corp of Engineers or national forests.
We have found that if you make a reservation you won't know until checkout when they ask for your Access Pass Number if they will honor it or not.
We have just gone on the assumption that it is honored at governmental campgrounds and we always found it to be true. We rarely made reservations. Even if you don't make reservations, the above web site will help you to find places. However, not all campgrounds accept reservations. Many are first come. Those campgrounds you won't find listed on the above site.
Another very reasonable way to travel, especially when you get into the Plains States, is to check for a city or county campground. The will cost a lot less than a RV park and we have found many good ones in our travels equal to a mid-priced RV park.
Too bad it has to be so confusing. Good luck!
