I would also screw twice there because that is the most stressed area; you don’t need to use such thick screws, better to use two instead. Of course, it also works with one screw and even stapling would hold, but in the end, it’s the most important area and eventually something will squeak or creak. Maybe not immediately but in a few years...... What I was still wondering is if you placed the bench across the room freely, meaning without any additional support except at the outer walls? I don’t know if that would be very visible but I would probably put a support in the middle on the floor. Maybe a bit further back, then you wouldn’t see it, right? I think a 2m bench would otherwise eventually squeak because it bends a little.