Find something that’s waterproof but breathable. Covers are great to block the damaging UV rays but unless they breathe they’ll hold in moisture which can cause all sorts of problems. Be sure to ask if the seams have been waterproofed. Additionally if you have a RHD drive car or double mirrors, be sure the cover can accommodate the mirrors.
I’d like others to chime in but I’d be concerned about leaving the convertible top folded up for extended periods of time due to moisture considerations. Dublin is a far more wet environment than California so I’d be sure to air the cars softtop and trunk area on any day when the weathers good. The last thing you want is the creation of more issues.