Also look up federal bridge laws, this says you get up to 20k lbs per axle 34,000 per tandem also there is a 37k lb for two axles. Difference being HOW far apart the axles are, to "bridge" or spread the load on the road bed. This is an engineer based design limit of the road.
Even if a manufacture rated an axel at 30k lbs, you can only out 20k lbs and legally run down the road. There are a couple of exceptions, but for those pulling towing carrying in the RV world, those exceptions will not work. At least from this forum standpoint. In type A MH bus chassis relm, you can get to 24,000 lbs on an axle.
I've been pulled over at 150% of my dump trucks manufacture GVWR, No overload ticket as I was under the bridge law amount. Altho about 1200lbs iirc my paid for license. Got a 10 day up license by a ton, sent on my way down the road.
aLL Leo's in wieght divisions care about is you having paid the tax, so damage you are doing to the road is paid for via registration.
Marty