This was the worst infestation in the trailer of mice. We took the shell out, washed itt with a soft brush and water, then water and a wire brush, the back to the soft brush and bleach mixed with water about 50/50.
This is the front panel behind the hitch, there were many nests, and pathways the mice had made, and the worst were to come- over the inner shell in the front...
Here I added in new insulation and screwed in 1x2 pressure treated lumber to act as an additional attaching point for the belly skin. Those thin beams would be impossible to drill in to. I also ran flexible piping for a future gray water tank to be added just behind the axles.