While we have never RV'd because they are just too few to find and rent, we have been to many national parks and nature trails. I read the
page you linked and I would agree with it. Full accessibility can be a challenge due to the things you note like grading, gravel or other barriers. I would strongly recommend travelers call ahead to ask about accessibility. Don't just ask, is it accessible. The answer is always yes. Ask specific questions about grading, site access, pathways, ramps, stairs, facilities, etc. Ask "what can't I access in a wheelchair?"
That question usually gets someone thinking differently. We rented a beautiful cabin this summer in Tennessee that we found online that was specifically listed as wheelchair accessible. The photos online all showed a lovely one level wooden cabin with all the amenities of home including a disabled bathroom and ramp to access the wrap around porch. We called to confirm all information and were confident this would meet our needs. When we arrived there was a 4-6 inch step to get into each doorway from the porch! We never thought to ask that question. We called the owner (from the porch) and he came out in 10 minutes with lumber scraps to build a makeshift ramp for us to access the door. Lucky for us, he was quite willing to help and was very apologetic and it worked for us.
My wife and I frequently say, "Putting a blue wheelchair sticker on the bathroom doesn't make it accessible".
Candy Harrington has
written more books recently.
I think she is a good resource for disabled travel.
The link I posted this morning was the most complete site I have ever come across about disabled parking/permits. It was very comprehensive. I was surprised to find out in NYC they don't honor any permits except a NYC resident one. We went to NYC a few years back and luckily parked in a public lot or we would have been ticketed and towed if we parked on a street. Some cities allow free parking for those with disabled permits. Again, a bit of internet research can help a traveler before they go.
I'm glad to help out where I can.
Ed