Ok First make sure the antifreeze is in good shape in both. Once that is
done fill the tank and add some stabil to the gas. While you at the
store buy a couple small trickle chargers.
Put down a tarp that is larger than the car and drive onto it to help
with moisture control. Even better would be to put down 4 ramps on the
tarp and drive onto them. That also helps keep the mice at bay. Just the
tarp would help with the RV. Put some moth balls under the hood and
around under the car. Put tire covers over the tires on them (nothing
fancy needed just something to stop the sun from beating on them). Those
will also help with mice. Same with the RV but you could also put some
in the compartments. Add RV antifreeze to the holding tanks and flush it
through the system as well. Shut off heater and fridge, and disconnect
the house batteries and the starting battery. Personally I would store
ALL the batteries in the house on a block of wood with newspaper and
baking soda under them below the wood and connected to the trickle
chargers. Plug the trickle chargers into a timer so they are only on 1
hour a day or a couple hours a week.
Change the oil if it is close to being needed, or if the vehicles have
only been run for short trips. That will get rid of the built up
moisture/acid in the engine. I would also buy some engine misting oil
and spray it into the intake with the engine idling. Then shut them
down. Give both a good wash and wax to remove the salt/dirt they may
have. I have done a wax job and then not wiped off the wax as well. Then
when you want to use the vehicle you wipe it down with a good wax/grease
remover and give it a good wax job then. Your choice there.

When you get back reverse the process.

Search on winterizing boat engines. Disconnect batteries and clean any
corrosion and put a little silicon on the posts to prevent corrosion. Change
oil and run a couple minutes to flush fresh oil through engine. The boat
engine we always pulled the plugs and squirted a  little oil in the
cylinders and cranked over a couple times and then put the plugs back in.
Store with full tanks of gas to help prevent moisture in the tank. The best
solution would be to have someone drive the vehicle every week or two long
enough to get it hot. It would solve the other problem you will have of
rusted rotor and brake drums.....

Check/get the antifreeze to around -40. Take batteries inside. If
that's a problem, at least take one cable off. Change the oil after
winter. Condensation, (moisture), can accumulate inside the engine
while it is not being used. Changing the after it sits will get rid of
it. (it's not allot. it's just a good thing to do after it sits)