I don't have the side skirts (Mates cupra does)but they do have a retaining strap on the inner.
Are people not replacing the covers correctly after removal or am I missing something.
Its possible that where the strap fastens on the inner that this piece could get damaged when removing the cover hence loosing it on a journey as the strap is not fastened in place properly. No ?
the strap you talk about is fragile and snaps off easily , about as much use as a chocolate tea pot.