Yes. 

I gutted and redid the entire interior of my first popup, a 1984 Coleman Columbia.  Someone said it was a good idea to insulate the walls since I had them exposed.  I didn't see the point of insulating the bottom 19 inches when the top 48 inches was canvas....but I did it anyway.  The mice really enjoyed the insulation the following winter  >:(

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You should use hard foam where possible.  Cut to size and fit as close as possible.  In ANY exterior gap/opening - put steel wool and use a can of foam in place (ie: Great Stuff brand) - insert the tube beside/behind the wool.

Mice don't like hard foam as much as fiber glass which they love to nest in....hard foam - no so much but can still dig though it....which is why steel wool is used. They can't chew/dig though steel wool!

If you can stick a finger into a gap/hole then a mouse can get in!

Another alternative: The owner of the big garage where we store our TrailManor says there is a big black snake that hangs out somewhere outside (??) the garage and Ben has never seen any sign of mice.  ;D  This is our 2nd year of renting the space and so far, so good!