Adding a vent to supply fresh air into the sleeping cabin?


I may use a stainless steel butterfly vent like the Sea Dog Stainless Steel 5" Butterfly Vent which costs $16.95 from Amazon.
Sea-Dog 5" Stainless Butterfly Vent
Stamped 304 Stainless
Diameter: 5"
Length (Fastener to Fastener): 4-3/4"
Vent Area: 2.91 sq in
I'd build a fresh air passageway in the galley.
Alternatively if I could find a source in the USA I might use a Hit And Miss Vent Cover which are readily available in the UK. Hit and Miss vent covers are available in many sizes and materials. One could be used to let in considerably more fresh air than the above butterfly vent with its 2.91 sq in vent area.
Some initial test shopping success! I could buy a Bulk Hardware BH00534 Stainless Steel Hit and Miss Vent, 229 x 77 mm/9 x 3 inch from Amazon UK delivered to me (the estimated full cost of the vent and delivery) for $21.55.

