I went ahead and got the 4" round vents with screens and I'm happy with the results with a removable cover that will keep furry critters out that inviting den space below the tank.

It went really easily just by bending the tabs back using a bent pick tool.

Here are some pictures for reference...

https://www.ventmyhouse.com/4-round-open-sc...item-4-rst-100/
Click to view attachment
Click to view attachment
Click to view attachment