G'day jj,
When we had our trailer tent camper, we would use a tarp over the top, 30x24.
It would give about 1.2 meters extra coverage along the sides and about the same at the ront, but over the annex kitchen en it would allow for 2.4 meters or so of shade and in wet weather this was great, meant the kids weren't boxed inside. Also if wet, there was plenty of room to hang the wet clothes and towels.
yeah it was a pain to put up, but worth it.
The below two pics are of a smaller tarp we had before the 30x24.
Here is a pic with the bigger tarp.
Our camper is to the left in the below pic under the tarp.
It was one of the heavy duty tarps with the D ring sewn into the edging.
Sure it use to weigh a heap and we needed to carry a ton of gear to use it, but as mentioned it did have it's benefits when camped for a fortnight or so.