I've had no problems with mine but then I live in the south....
My comment was 'tongue-in-cheek' - I'm not expecting it to leak but it was more for convenience when parked up rather than having to put roof up just sling a cover over... or when parked with roof up to protect mohair from bird crap!
Ah, I see... a good idea to have a cover for the roof, in case you have to park under trees.
I'm 45 minutes from Poole - but my S5 is 6 or 8 weeks away.
If you don't have a solution by late Feb, let me know :-)
Will