You can have one that hoists with a spare
halyard. Your
sailmaker will make one to size.
Make sure it has a long line zig-zaging the whole thing top-to-bottom that you can then make tight at the bottom end. Otherwise the cover may start flogging in the
wind, which will chafe through the sail's fine threads in no time. You may end up with more damage than done by the sun this way.
A cover like this is also great for your roller furled genoas if you spend time in places where there is a lot of sun even if you have already a
genoa sacrificial strip.
b.