The mice and squirrels loved the pure peppermint oil on cotton balls. Moved it around. Used it for nests. Found at least 300 nuts under the couch. 2 or 3 nests. Tried the light trick. Never shone through. There was sort of a maze of metal work underneath that prevented the light from getting out. Reversed a shop vac and felt the air coming out. Stuffed the area with aluminum screen scrap from inside. Pushed through in a couple days and found a new squirrel, I think, nest. Stuffed screen scrap everywhere and most infestation stopped.
Got rid of the RV that year.
Got all the screen scrap from a small hardware store for free. They were happy to get rid of it.