Peppermint is not going to deter mice from entering your home. To manage a mouse population, you'll need to snap-trap, eliminate their access to whatever food source they're using (containers, cleaning up, making sure they're not getting access to pet food, etc.), and the most important part - Find their entrances to the structure and block those with unchewable material such as steel wool, hardware cloth (welded wire 1/4" squares), concrete patching, etc.
I don't recommend using poison because there's a strong likelihood that some of the poisoned animals will die and decompose in your walls or crawlspaces, etc., which then leads to another health-concerning problem.

Thank you for your prompt reply. You have convinced me that peppermint oil is not effective.

Here is another scenario. I have a camper van that I park outside during the winter. I have heard that mice can get in the engine compartment and eat the electrical wiring. There is not really an effective way to prevent mice from getting into the engine compartment. I imagine snap traps might be an option. What about bait boxes? Are they effective? I see them outside commercial buildings.

If mice eat the bait and go off to die are poisoned mice a danger to neighborhood cats that might either catch poisoned mice or eat dead mice?

Are there other options you would suggest?

Thant you,

Tom Wykes

I would recommend parking the camper on a hard concrete surface, preferably away and apart from rodent habitat. I suppose house mice or non-native rat species might move from a structure into the camper van, but outside-stored vehicles tend to incur damage from either non-native rats or any one of several native rodent species that are otherwise using the area as habitat and then discover the shelter and food opportunities within the vehicle.
I would focus on preventing or at least reducing likelihood of your van being in an "ocean of habitat" so you can reduce likelihood of discovery and occupation by any rodent species. Yes, snap traps can work, but once you're having to kill animals inside, it's quite likely that they might be nesting in places you can't see, etc. In general yes, poisoned animals can potentially be killed by either wild or domestic animals and thus harm those consumers via secondary poisoning. Some (some?) companies might be setting bait that is "non-toxic" but purports to kill by clogging up the consumer's gastrointestinal tract and killing them that way. Whatever lethal bait you might choose, the warning to not have dying animals seeking final shelter somewhere deep within your home OR vehicle still stands.