It happens that Jon Parker formulated :
I intend to use a 3-position switch to enable me to easily switch the battery
positive to the solar charger, or over to the 12v outlets, and to prevent the
outlet from receiving power when the battery is connected to the charger.
I'll need some sort of weatherproof box for exterior wall outlet of course. I
expect I'llneed to put a suitable fuse in the positive line, around 6 inches
from the terminal, 10 or 20 amp should be fine I think.

There is no obvious need to switch the power between charge and the
sockets?

If I were considering doing this, I would be installing a mains powered
12v (13.8v) SMPSU - do you not have any mains power in the garage?