I got the cover for my Fastback at Wal-Mart.  It was the 18-23 ft. one (I do believe) and it fit rather nicely.  It was the econo model, and it proved to be just that.  It was cheap, but it worked for the 2 years of it's 3 year life.  Hint: Don't let your cats get on it, climb on it, or sleep on it.  Not only do their claws tear it to shreds, their weight slowly pulls the fabric apart as the cover gets older.  It was only $30, which is good cover for $15 a year.

Or you can go for the ones in the VW catalogues.  Got one of those for my Westy and it is still in good condition, although I haven't been using it lately.  It is water resistant (not proof) and is breathable.  It cost $99 and is worth it.   :lookaround:

In case anyone was curious, the $20 cover from Wally World fits very nicely, but it is NOT water proof, I think it works well for showers, but for all day rains it seems to get soaked then procedes to let in as much water as it keeps out, guess it's time to ante' up and get those window rubbers

VWTrav