Rodents... Awww, but they look so cute what with their itty bitty little feet, big ears and all.
Mice can fit through a hole as small as 1/4" in dia. and rats 1/2" in dia., as long as their skulls can fit through. Rodents are pretty good at climbing too. Besides chewing through stuff, the feces & urine are a problem and rodents can carry many diseases and you should take the necessary precautions. Enclosed underbellies make a cozy place to nest. Solid material like metal or plywood would be best to cover holes but not always possible. Lots of chemical treatments available. Poison not a good idea -mouse/rats are better. Don't know if the steel wool method works well.
If you go looking, there's plenty of holes, cracks and gaps in RVs. Often in floors but also places like slide seals & shore power cord opening. I sealed up a LOT of holes in our floor. Some looked like they used a chainsaw and in one location, they hacked clear through aluminum floor joists.
I built a house once and a field rat chewed through the exterior wall plywood. I put in a new piece of plywood only to find that it chewed through again in the same spot. Found it in the basement and thought I'd throw a cardboard box over it. It stood on it's hind legs, bared it's teeth and let out a blood curdling scream. Bad idea. I then resorted to poison only to learn that a dead rat hidden behind a wall somewhere does not smell good. After that, it was traps...
