5 bolt valve cover leaks

I know welcome to the crowd with valve cover leaks but I welcome any helps,I tried buying the moroso rubber gaskets sandwiched with steel inserts but we still get leaks on the lower corners(firewall side),Covers are fabricated aluminum,So any suggestions would help,Should we go back to cork????? I put the gaskets on dry like the instructions said would rtv help or is that a no-no--Thanks Steve