FYI, 2"foam underpinning R-Factor is 9, average straw bale R value is 28, at least.three times the insulation. It must be kept dry though.
If you have any trailer/ morotorhome/car/tractor idle it is an invitation to rodents. That is a seperate issue from insulation and warmth.
I store my AS in an all steel building with concrete floors, I still have to manage for rodents.They nest in cowling of the cars and in my friends Motor home and in the dash of my tractor which are also stored there, it has little to do with straw and the world to do with insulating materlas and the world to do with them finding small, confined dry spaces.
You will have to deal with rodents.
If I were wintering Colorado in an AS I would buy enough bales and bags to stack around up to the bottoms of the windows and I would loosly fill bags and put them on the top, as previously mentioned an AS is not designed for full time living, but with a little redneck engineering you can make your stay more comfortable, all be it not fashionable.
Explore the use of straw bales in houses if you need more understanding.