Ahhh, this was Rotterdam? I though maybe Rosmalen - Rosmalen is smaller, yes? So the tent was only an enclosure that led to the locker rooms? At some small tourneys, they don't have enough space at the club, so they have some temporary facilities. Some of my friends go to a tourney in Liverpool that is completely temporary - ALL tents. In a field. Marat Safin, showering in a tent and eating burgers from a van.
The tent picture was made in Rotterdam. Some others were taken in Rosmalen. Rosmalen is not really a smaller tournament, because WTA and ATP are combined. There are a lot more courts there and it's in the open air. And Rosmalen makes use of, as Via said, solid bunkers.
Now Rotterdam is indeed a temporary tournament, but the Ahoy complex is very large, so there is no need for tents for the players to stay and shower in lol; they have good facilities.