Whether it's legal or not to live on your own land in an RV will depend on where you're located and whether you're living in a town, city or in a rural area or way out in the woods.
If you're living in the RV in town or in a city then the city or town could have local laws regarding the legality of living in the RV on your land.
Some cities and towns make it illegal or against their ordinances and zoning laws to live full time in an RV on your own land and could fine you which isn't right but that's the way it is in the so called land of the free.
If you're living in a rural area or way out in the woods away from neighbors then it's likely legal and even if it weren't nobody is likely to bother you or care about it.