Yeah trucks across Europe are generally pretty good, primarily because in many countries it's illegal for them to be in the 3rd lane (except sometimes in heavy slow moving traffic).

Overtaking from the right, or undertaking, is often illegal also, though. So while I agree that it should be ok, strictly speaking it isn't.

What is legal is to overtake on the outside, move into their lane, then the inside lane, then slow down so they overtake you. Rinse and repeat, count how many donuts you can draw around them before they move over.