Bought my last trailer in 2011, first spring after I discovered mice had been in my trailer over the winter... :M
That spring I inspected under the floor deck and this is what I found
and this...
There were a few other openings but I sealed them all up that spring and never had a problem again. :C since owning rv's I have always used mouth balls & bounce sheets, honestly I really dont think they do much but I will continue to use them.
We have also had problems with both Red & Gray squirrels. 2 summers ago they have chewed a hole in my old shed doors and got into my lawn tractor engine and other important things. They did some damage, I ended up replacing the doors. I also for about 2 weeks straight used a "Have a Heart trap" where i was removing 1 per day but they kept coming... Cut down my Black Walnut tree last summer and this helped somewhat, If I continue to have problems I will look into the Squirrel pole idea! :C
One other thing of note and as mentioned, before ALL of this we had a indoor/outdoor cat that hunted everything! ... never had any problems with rodents, don't underestimate a good Cat!
Mike