You can be ok on a weigh bridge but still get nicked for overloading your rear axle.
Just because you have a xxx payload dont mean all the weight can be on the rear axle.
Paul
Usually more danger of overloading the front axle as vans are designed to have the weight centrally located in the back, not tight up against the bulkhead. I assume this because my van was weighed and just within the limit. The tank is set back well from the bulkhead but the front axle was very close to its limit.