Your mfg will have a suggested weight in your manual or posted on the placard on your rv....
but that's with the original stock tires only...
Also, the sidewall of any tires made in the last decade will have the max load and max psi stamped on the side of the tire...
The tire stamped psi is what I normally run my rv's tires at... gives
max load carrying capacity and
max mpg (because it gives minimum drag) and
harshest ride (but no ones every riding in the rv to notice
)