Hey, I learned a trick last weekend to keep mice away that you could probably use. Fill the edges and cracks to the out side with steel wool. The mice won't chew through it to get in like the will with insulation. Places like around windows and doors behind the trim.
A perfect spot to do it would be when you connect the new addition to the cabin. Put it between all the new framing and "old" building, and then put your sheeting over it.
Have you looke into the mowers to pull behind the wheeler? I'm not sure how much they are put might be somthing to look at too.
