I have a 1988 3.2 Carrera Targa which I drive every day and I keep outside. Firstly I covered it with a Halfords car cap which kept the sustained, overnight rain out, but I now have a Covercraft Noah fitted full cover so that the whole car is protected almost as well as keeping it in a garage. It's a bit of a pain taking it on and off but it becomes a routine and you just get on with it. You can put it on wet or dry and even dirty as long as you clean the cover fairly regularly.
Also, you can order these from www.bigskycarcover.com
in the States for half the price that they cost here - even with shipping! They are for left hookers but that only affects the mirrors slightly so no big problem.
Thanks for those replies. Putting a car cover on all the time seems like more than a little pain in the ass but I suppose its time well spent if you love the car.
Can both of you privately post me some pictures of your cars - love to see what people drive.
To be honest, it's really not that bad once you've got a system going - I roll mine up from the back to the mirrors and then the same from the front. Then just pull it off the mirrors and store - just a simple reverse process to put back on - probably takes no longer than parking your car in the garage.