Chickad - The web site Allstays will tell you for free what the restrictions are at Public RV parks are around the US. I can tell you that lots of CA State Parks will not let you in. Many because you will not fit. I volunteer at Cuyamaca State Park in San Diego County and I would be very very hesitant to try and get a 36' motor home into one of our spots. Our campground was built when RVs were normally much smaller.
It is certainly true that there are many public parks you can get into, but in my experience it is not true that you will have "no problems" as posted on this thread.
The easiest way to look up length restrictions is an Ipad-Iphone ap called Campmore. It will tell you in a flash.
Country Coach 42' Affinity
2013 Jeep Wrangler Unlimited