If you move the vehicles frequently and are in urban areas mostly at night you will likely be ok. The desert and mountain campsites will be the likely areas where you will need to leave the hood open and try to park away from bushes and other ground cover.
Those electronic devices, mothballs, poison have not helped in my experience. The One Bite poison does kill them but does not stop the nest building and wire chewing immediately like a snap trap does. Plus you must wire it in place or they will haul it off for winter/later usage and still chew the wires.
I use large RAT snap traps and even so have had to finish off the pack rat about 1/4th of the time. You will have to check the trap each day and deal with the remains or half dead pack rat.
I am currently experimenting with coyote urine. We will see how it works vs snap traps over the next weeks.
IF you do need to remove a nest or clean up after any rodent, wear disposable gloves and a P95 face mask (hanta virus kills). Read up on hanta virus
linkBTW: I keep my 5er in a remote mountain site in summer that is overrun with pack rats, mice, squirrels, etc. I keep the RV pretty well sealed but they still nest and chew wires outside and on the vehicle if I do not drive it each day.
2nd BTW Pack rats use dog feces and cactus to keep coyotes and cats away from their nests-just so you know when dealing with what looks like a pile of sticks under the hood.