Hi...My first post....
Peppermint oil drops mixed with water in a spray bottle, you can spray inside and outside your trailer, will keep SPIDERS away - but not mice as far as I can find. It is not harmful, and smells good. Spray as needed. You can put a drop under your tongue after dinner to help digest your food, and freshen your breath..
I sell oils, and in my book for mice, they recommend a blend called Purification. It has several oils in it, but one of them is tea tree oil that is probably the easiest to get at some stores. Tea tree oil can also be used for sores, cuts or burns as it has antibacterial qualities, plus if your nose is stuffed, if you sniff the bottle, or put a few drops in boiling water and a towel over your head and deep breathe it will help unplug your sinuses and lungs.
That way if you buy the oils to use for your pests, they won't go to waste.
I am not a Dr. but I do believe in the power of essential oils.
If you are unsure, you can look up their uses online.