I looked at buying some vented hatch lids from the US, but didnt like the fact that they were aluminium lids only and the freight cost.
I couldn't find anyone here in Oz interested in venting the spare lids that I had.
So I thought I'd try it for myself.
Bought a vented sheet from RodLouvers.com
Then made up steel former top and bottom that fitted over the louvers and shaped them myself.
Took the hinge and clip from the old lids bottom of photo and brazed them onto the new lids.
The louvre sheet was a bit short so I had to add a piece on top, but overall it turned out ok.