If you have pets and or allergies stay away from off the shelf sprays.
Peppermint Oil does work. Has to be 100% PURE oil. Pricey but works.
IMHO it's more prudent to find out HOW they are getting in.
What I found was that when MH's are built there are a lot of exposed over sized holes where they run wires pipe etc. They are small and hard to see but they are big enough for mice to squeeze thru.
Go out at night and turn the lights on in your MH and crawl underneath. You will be 'shocked' at how many places you will see light seeping thru. Use the insulating spray called 'Stuff' to seal the openings.