It happens all over the EU. Police will randomly select semis and camper vans and ask them to follow them to a weighting station. For example in Germany they are spread out along the Autobahn - same in France and NL.

The weight is usually determined by 4 scales (1 for each wheel).

Then they look at your papers which also includes information about max load at the front + back.

If you are over weight you have to get rid of the additional weight and if you can't they will seize the car. You get fined. It does happen.

It happened to me twice in Germany, once in Norway and once in France.