Those vents can be plastic too. My Fuzion has metal ones but my older Skyline had plastic ones.
They do help if used correctly. The vent mounted high on the wall (normally on driver side) is opened facing forward like a scoop. The lower one (usually on pass side) is opened facing to the rear to make a kind of vacuum to exhaust air.
The theory is, , , gasoline fumes are heavier than air and will settle to the floor. The high mounted vent scoops fresh air into the garage from above and the lower mounted vent exhausts fumes out of the garage. This action will continually move air thru the garage and keep dangerous situations in check. These vents will not handle leaking fuel fumes and are only useful for clearing fumes from normal gas tank venting.
Today's fuel injected engines are much better at keeping fumes contained because after you have shut down the engine the fuel system really has no openings to allow fumes to escape except for the fuel tank cap.
Older equipment with carburetors are much more messy and allow a lot of fumes to escape. If you have one like this it would be wise to shut off the fuel and run the engine out of gas and then close the fuel tank vent most of these machines are be equipped with.
The constant "shaking" motion our toys endure as we travel combined with changes in altitude and temperature will cause gasoline tanks to vent fumes. Using those side vents on our haulers can prevent a bad situation for us if we use them correctly.
2015 Jayco Precept 35UN
named
"Free Range Chicken"