I use a very light smeer of Permatex #2, about as little as you can put on and say it's on there. not enough for any to squeeze out but almost. To much and it does make a gasket squirm, used correctly it's wonderful stuff!
I prefer to use a gasket adhesive to stick a gasket to the oil pan or to the valve cover. Use Permatex #2 on the other side. But I often put valve cover gaskets on dry to the head, then they're reusable many many times over. If the cover is straight you shouldn't have any leaking issues.
Grigg