Critters and Air Filters
Over the years I've had several air filters chewed up by field mice. Here's my solution.

THis is what my air filter used to look like after the RV had been sitting for a while. It's parking spot is on gravel, but there is high grass and shrubbery nearby.

This little piece fashioned from a piece of aluminum flashing has solved the problem.

Step 1 is to loosen the clamp that holds the air intake in place. The air filter is just past the clamp.

With the clamp loosened, it's easy to pull the front-end of the air intake from its hole above the radiator.

Place the piece of aluminum flashing over the opening of the air intake.

Snap the air intake back into place and tighten the clamp.
Important:
Put a note on your steering wheel to remind you to remove the aluminum strip before starting the engine.