hmmmmmmmm............Since the crankcase and valve covers are all at a positive atmosphere, you would expect, if anything, the pressure would push the gasket out past the lip of the valve cover. Is THAT what's happening, or are the gaskets finding their way into the rocker gallery??
If they are going into the gallery, I would suspect the flatness of the aftermarket valve covers where they mate to the head. If there is a slight angle to the mating lip, especially closer at the outside of the lip than at the inside, they'll pop the gaskets into the rocker gallery in short order.
The fix? Try the fake 4-cam covers you have and see if that cures it. If not, I might try the Berg stock, vented covers. If THAT doesn't work, I would glue the suckers in with Permatex blue gasket goop.