My objective was to build something quick to install/remove, quick to use and without the requirement to punch holes in my RV.
An interesting solution was to emulate an existing solution available on the market with a pleated curtain.
The "commercial" solutions are too expensive. This one will cost you less than 15 Euro.
I bought from IKEA, 4 very chip pleated curtains named Schotis (2.90 EUR each), two 1m*8mm alluminium pipes (Leroy Merlin) and draw some objects compatible with the Fiat Ducato cabin (mine is X250 2014 but I am sure that it fits well in many models).
In order to Connect the printed objects with the pipes, I used two 6MM screws.

You must be very carefully when drilling the curtain. It is made of rigid paper so it is very hard to drill quickly and each element must be drilled separatelly.
In the current version the bottom part is simply lean against the dashboard as you can see from this picture taken from inside the cabin.

Probably in the future I will modify it to use additional two pipes for the bottom as well. And probably I will also change the curtain model with something more expensive or rigid.

However, for sure some pictures of the result is better than one thousand words.

Laterals are simply cutted following the window once opened. The glued border (those curtains made by Ikea have some glue on one of the two sides) is connected under the lateral seal.
I draw also two clips to sustain the curtain when opened.

Please consider that this is a work in progress. As I do not like the two pipes visible at the top of my cabin, I will draw some cover in order to give a better look to the RV cabin.
You can print all STL files using simple PLA. Consider the opportunity to change it in case of different dimension. If you want to evolve this subject you can but, please, take into consideration to leave the original verion or a link to the thingiverse home page.