I put back all the back mods on the megane :
The mini open tail stays strongly on the car, only with half a dozen squares of double side tape per side and strong tape. Sadly the black tape doesn't stay as well as the gray one, the reason is that the painted chloroplast and black tape are getting very hot, but the rear door blocking the rear wheel skirt do secure the whole thing.
I consolidated the rear cover with some expanded polystyrene :
The polystyrene sheet is taped to the cover with some double side tape. Once I drove 200km (124mi) with 3 tree leafs inside the covert and they stayed there
I also rebuild the front :
The goal was to lower the lower part and to lower the stagnation point :
You can see a piece of expanded polystyrene which consolidate the external part. It's taped to the chloroplast with double side tape and pushed frontward by the front spoiler.
The middle part has also been consolidated with expanded polystyrene pieces :
Denis.