I have the same situation in reverse, I have the 5exi in the garage and the MGF on the drive. I bought the Lightweight Outdoor breathable Car cover from Classic Additions for £93.60 delivered.
I was swayed by a combination of the price and the fact that the cover had won the Pactical Classics Best Buy Award. For the money it's one of the best purchases I have made. Excellent quality & strength, 3 adjustable securing straps, carry case and the rain just rolls off the surface.
If you want to contact them www.classicadditions.co.uk
or 01938 561717