I've one for my Boxster that is official Porsche cover but isn't stretchy and was about us$100. So, somewhere, there's an official Porsche indoor (lightweight) cover _other_ than the one on the above link.
I offered this last winter and I'll go out on a limb again, I can drop by your places and start and drive your cars for you. I don't charge too much. (Just air and a hotel).