I live in an area that has numerous rodents of various types. I've been through this, including having 3 Honda trucks attacked by rodents and pulling 5 gallon buckets of pack rat nesting material out of heavy equipment. Took me several years of painful trial and error before I figured out how to keep them under control enough to not have vehicle damage.
You just cannot keep them out of vehicle engine compartments and other open areas. A typical field mouse can squeeze through a hole the size of a dime (~12mm) and they can climb and jump surprising distances. They can also chew though any plastic/fiber/wood that they can get their teeth around. Their droppings and urine produce smells that attract more rodents and will linger for months if not cleaned up with ammonia or bleach.
They only reliable way to keep them out of vehicles is through bait boxes with commercial poison in it. Not the stuff you buy at the hardware store. You need to buy from a pest control place or other commercial provider, which means it only comes in 5-10lb buckets. The two best poisons are bromethalin and bromadialone. Both kill with one feeding and thus prevent the rodents from teaching each other that the bait is not good to eat. Rodents are very good at teaching their young and other rodents what is good and what is dangerous. Neither of these poisons is safe around pets, in that there is no antidote to a larger dose. Eating poisoned rodents is not an issue since the ingested dose is small enough to not have an effect on a larger animal.
Different types of rodents prefer different types of bait. I use a combination of a sweet sugary smelling bait with one that is grain based.
The other option is to get a couple of outdoor cats that have a strong prey drive. Some shelters will offer "barn cats" that are unsuitable as pets. Takes a bit of work on your part to teach them to stick around rather then run off, but it works well at keeping the rodents away.
To keep them out of air intakes you need thicker wire mesh or for smaller openings stainless steel wool is something they will not pull out or chew through since the strands are razor sharp.
Most of the common do it yourself methods of control simply don't work. Look at what large commercial operations that deal with food / animals, etc. do. All of them use bait boxes and poison.
I wouldn't use mothballs inside a vehicle, as they contain naphthalene, which is a carcinogen and can cause red blood cell destruction in people with a certain gene. Not stuff you want to be breathing. Not sure if modern moth balls have the stuff these days.
I've used the Honda pepper infused tape, but it's hard to know how well it works. There are plenty of other wires for rodents to chew on and they have in my Hondas. Worse part is that most of the wires are in a plastic loom, which means the wires are often chewed off right at the connector, making simple repair almost impossible.