I'd do the following:

Use marine oil instead of normal motor oil. Use something that is
designed to cope with sitting around or having water in it more than
automotive oil.

As part of the service interval, I would say that the car should be
driven on a highway for an hour each month. Not idled to operating
temp or moved from one side of the garage to the other but driven on
the highway with the loud pedal all the way down. Maybe once a month
is too much, but if the car is driven at all in the month, it should
be driven on the highway as well.

Water collects in the oil if the car isn't run under load for a
period of time long enough to boil it off. With most SUs, gasoline
also collects in the oil. If you park the car for the winter, you
don't collect this crap in the oil, but if you drive the car 2 miles
each weekend you're going to put all kinds of crud in the oil.

A decent oil probably only needs to be changed once a year or even
once every other year, as long as you get it hot (highway running)
from time to time.

Change the brake fluid to silicon dot 5. It would pay to completely
flush out the existing brake fluid. Dot 5 is not great for normal
cars because it gets air bubbles in it, but if the car isn't driven
much it is ideal. Flush the fluid once every 5-10 years with dot 5
or once every 2 years with dot 4.

Change (or at least look at) the plugs every 2 years or 10,000 miles.
Adjust valves and remove / inspect / adjust the distributor and points
every other time you look at the plugs (20,000 miles). Replace the
tires every 4-6 years even if they look okay since they can rot away
and still look good.

Replace the radiator fluid once every 3-5 years or if it gets funky.
There are ways to test it which might be worth looking into. I'd replace
the radiator hoses every 7 years if they need it or not. Same goes
for belts and the battery.
chris