Valve Cover Gaskets for Fabbed Aluminum

I have the same valve covers on my racecar. I have the Fel-Pro 5/16 thick gaskets to help clear the intake runners. I used black silicone to glue them to the covers & let it set up.
They have been on the engine for three years.
I check valve clearance about three times a year.
No leaks yet, I run an open breather in both valve covers.