If you want you car to be protected from the elements but like me you don't like covers that come into contact with the paint work, ie scared of that wet n dry effect, then these are ideal. You simply drive upto them, then pull it up and over the car. They are superb!
I have only used my inside a barn to keep the dust off, but they can be used outside although you'll need to fix them down (I have some U brackets somewhere that I'll throw in if I can find them)
I bought mine from these guys:http://www.canvasandnylon.co.uk/Perambu ... 20copy.pdf
Its the 17x7 Poly one. So will fit a Z4 with room to spare! It was £420 new, I'm asking just £275 no offers
! Even when folded it is large, so you'll need a large van to collect, or best bet a car trailer that you can strap it down to. Collection only from just south of Milton Keynes.