[GordMay]

Your (proposed) “dedicated” 12V outlet wouldn’t need to be shunt switched - just connect it in parallel with the Blocking Diode (Ed’s “isolation”) ahead of the disconnect (which is effectively, a permanent “shunt” connection). The outlet will always get it’s power from the Solar Cell, but will only be able to power devices rated less than the Solar output.
This is tough to put into words, when a very simple sketch would be so illuminating. Have I made it clear as mud?
Gord