[stoppingdown]

Thanks for the excellent feedback, as usual. As for the stones, fortunately there are no stones on the road, as the road is not gravelled, but asphalted. Since it's a road reserved to hikers, bikers, and a very limited number of authorised vehicles, it's not maintained with the usual standards and there's no smooth asphalt (that would not make me worry), but - especially in some places - is full of  irregular"patches".

 

In any case I'm also considering an alternate approach: put into the trolley everything else than the big lens (such as water bottles, the binoculars, the emergency kit, etc...). Might be anyway an effective mitigation of the overall weight on my back.