Wow, thanks for all the great suggestions guys.
Some info. Car is a 2009 Toyota Venza. Battery is under the hood. Will be in a garage enclosed on 3 sides, 'open' front [locked bars]. We brought a car cover for it.
We just had the oil changed, we use Mobil 1 synthetic oil in this car. Additive still necessary??
Will buy one of the gas additives suggested. We will do the diesel soaked rags, and will scatter rat poison around under the car. Will try to find dryer sheets.
No one will drive the car, no family close, and they don't even sell premium gas here, we have to go into San Cristobal to buy that.
a. if your garage has a concrete floor then you should position wooden slats, like plywood under each tire to keep them round. Easy to do, just lay them down and drive onto them.
b. dryer sheets(inside) will work with the mothballs(outside). Diesel is flammable and will evaporate during the time you re gone and then there will be no mal-aromatic buffer between your wiring harness and rodents.
c. take the battery out, put it in the house in the closet, on a piece of wood. It should retain its charge if nothing is sucking off the current. Remember batteries in the store are built several months before they are sold and they still have 12.6 volts in them when you install them. Even the car battery is disconnected from the time it was built in Japan to the month it spent on a boat getting to its destination in North America, so it is not going to hurt anything.
d. poison may work and it may not, disconnect your air cleaner and stuff a plastic bag in it to prevent rodents, mice in particular, from trying to make a nest in the intake. Roach spray works well for beehives, hornets nest and insect infestations.
e. 1/4 tank is good so if it does go bad which is plausible because no one knows the quality of local fuel in any event you dont have more than 4 or 5 gallons in there. But it will take a long time for fuel to go bad like 3 years or so.
f. my neighbor put me onto an alarm system he has on his cars, the Viper VSM-3000. It has a GPS or satellite link up which, listen to this: Allows him to start his car remotely from anywhere on the globe. He said from New York he can press a button or call a number and he can start his car sitting in his driveway in Central Florida. Plus the system informs him of the exact GPS coordinates of the car. Might be useful to you.
g. car cover is useful to prevent dust buildup and shield any exposed areas of the car that may suffer from sun-bleaching which could crack the dash, or fade the paint.