Well a few things to check after work tonight.
What really gets me with this is I've covered every inch of the trailer with my nose on the floor and can't localize where the smell is coming from. If I run the fans with windows open smell goes away, but closed up overnight, it's back.
Previously owners said no pets ever and I've looked for discolouration on the wood inside and out of cabinets and storage areas and not seeing anything. I've opened everything I can access and no signs of mice. No carpet.
Fridge and freezer works but I'll take another look there for coolant leakage.