If red team place wooden barricades at the bottom of the trebuchets they don't turn at all. I try to spam firebombs at them but they always have enough engineers to make it impossible for blue team to do anything. Plus the engineers can crouch underneath parts of the trebuchets and block themselves in which makes it almost impossible to hit them with anything.
It almost always seems to be the same guy doing it and he's always running fireproof and being a dick in chat. Really boring to go up against.