You run a good composite rubber Fel Pro gasket and simply take the cover off to do an oil fill.
I'd rather not have to remove the valve cover. I'm currently using the composite Fel-Pro gaskets and had a hell of a time getting them to seal... still had to use silicone. That might have something to do with the stamped steel valve covers I have now. Maybe the cast aluminum ones will seal better?
1968 Impala SS