Overflow leak - gasket placement?

Currently running two bulkheads through the back wall of the tank for a overflow - I have it:

Bulkhead - gasket - tank wall - overflow box flush - gasket - nut.

I read some people put both gaskets against each side of the glass - not by the nut? The leak is coming from the threads of thre bulkhead I assume down behind the overflow box - but I also get some inside the box between the nur and threading. I tried tightening once, and researing once.

I'm worried if I try the gasket between the OF box once my plumbing goes in it may put pressure on the bulkhead since the box won't be flush to the glass?