You could use a tarp attached at the corners and guyed down I suppose. The Camperlands one mentioned above has side screens that attach, i've just got the normal sun canopy but not used it yet.
I've got the Camp-let sun canopy and am not very impressed with it to be honest. It collects puddles of rainwater, and looks a bit sad and saggy to me. I'm pretty sure there must be a more cost-effective solution.
The day room is very versatile as you can zip up all four sides so it looks like a gazebo. Features include 4 Roll up Doors, two covered PVC Windows, Two covered mesh Vent Windows. Most sellers include canopy poles so you can turn any one of the four doors/openings into a sun canopy.
It comes with a groundsheet, ( we don`t use ours).
Not been charged to date, but some sites do. Just tell them you have a gazebo as trying to explain what a day room is sometimes is like trying to explain you have a TT/FC and end up booking it as a tent as it easier.
We check before we book to make sure we are not charged.