Valve Cover & gasket question

I've had better luck getting steel covers to seal up. I have Mopar Perf. aluminum covers on my 360 now and usually I say no sealer but I tried Fel-pro rubber gaskets first and they wouldn't seal up good at all even though they've worked good on other applications in the past. Then I tried cork gaskets and they sealed better but still leaked some. I finally used RTV on the valve cover side along with the cork gaskets and they seal good. Oh yeah they are extra thick gaskets I bought at Auto Zone. Can't think of the brand right now, sorry. I've had the best luck on several engines with factory ribbed rubber gaskets that have the steel insert and don't use any sealer on them.