[RedDevil]

Mind you; I used the protective foil, not the Lexan itself.
I even picked the size of the sheet carefully so that I could make 4 covers out of the foil

The Lexan is not wasted though. I will use it to block the grilles, protect the fog lights and if enough remains smooth out the cavity under the indicators.

The wheels look best at a distance. Close by it is obvious that they are covered, and as it is just not 100% perfectly smooth it looks cheap. But then it WAS cheap - the Lexan was just 10 €, and the foil would otherwise have been thrown away.

I was worried about water getting trapped between the cap and the foil;, but have driven through some rain and puddles and none of that went in.

The foil folds over the edges of the hub cap.
You need to make sure that the cap still snaps in place toghtly, otherwise you have to grind it down a bit to make room for the foil.
Luckily I did not need to; they still snap into position firmly.

Check your tire pressure before you put them on - they need to come off now. Did not want to make a hole in the foil, afraid that will make it rip.