Anybody come across this before

[Steptoe]

Feck off! That's blindingly obvious though fundementaly flawed if it was applied in it's simplest form.

Blindingly obvious ?? I only mentioned it because of all the replies stating that seals would blow if the boxes were sealed in the way the box that you have. All i was pointing out is there are other ways.

Flawed ?? A breather hole is only a breather hole no matter where it is located.