Running 240V wire under mobile home
I assume by your question you want to run a 120 volt line and use the Level 1 charger that comes with the car.

If you are going to the trouble and expense of adding a receptacle circuit I would highly recommend a 20 amp circuit not a 15. The cost difference is small and takes the same amount of work to install.

At a later date it could be easily converted to a 20 amp 240 volt circuit to accommodate a Level 2 charger that will charge your car in 4 hours or so.

The smallest dedicated EV charger for a Chevy Volt will need a 20 amp circuit not a 15.

On the Clipper Creek web site you can choose your vehicle and it shows you the recommended chargers.

Normally, the larger the charger (higher amperage and voltage) the higher the cost but the faster it charges.

All that said, to answer your question, under the trailer and outside you should run PVC conduit to protect your wiring and survive the elements. Also, PVC is the easiest for a novice to install. NM cable can not be used in a wet or damp location so you will need to run THWN rated wire from the breaker box to the new receptacle in an approved conduit like PVC. You should run #12 gauge wire for a 20 amp circuit pulling 3 wires colored black, white, and green.

If you are going to hire an electrician to assist it may be just a few dollars more to have them do the whole job. Consider this.

Good luck and stay safe!