Susie R/T
You are doing the right thing with the mice motel.
I currently have an ex-mice motel on wheels, no matter how much cleaning you do, every once in a while on a hot day you get a hint of mice.
This is after ripping all the upholstery out but the dash pad.
Painting the floor with por15, new seats, carpet, and painting all the plastic, etc.
I swear that smell will never go away 100%