What’s the best way to find RVs for rent where you can live in on the owners property ?

In MOST states, that is illegal.

in SOME state, yoiu cannot use an RV as a "permanent" residence. In other states, you cannot live in a "temporary" shelter (like a tent OR RVon a permanent basis.

Unless the property is zoned for that (i.e. a campground) , people cannot live in RV's that are parked in a residential area.

No one is ever permitted to live in an RV on a residential property.

most people aren't going to rent you an RV to live in it.

There are some RV rental services, but they're meant for short vacation rentals, maybe a few weeks at the most.

Most places have zoning codes that prohibit living in a recreational vehicle so its not really a common thing.