would ten times over risk gas theft over water condensation overnight in
half-full or nearly empty tanks.

I have a Mooney so filling the tanks is a rare event (7 hours of gas is
way more than I need and I don't like pulling a yaht around with a
Corvette). I generally keep only about 10 gallons per side when parked.
I park outside and have yet to see any water in the 6 years I've had
the plane. Maybe the fact that a Mooney technically doesn't have fuel
"tanks" makes it different.

-Robert