I don't have a problem with storing a piano in a garage but with
caveats.  I have many pianos in my stash and among those I have
restored that spent a decade or more in a garage.  I have stored
some in self storage "garages" and have not had problems.
A garage is far better than a garbage dump.

I would need to make sure that the garage is dry -- not just the
floor or roof, but the air.  If there is mildew there, then things
are not dry.

Also, are there vermin?  Keep all mousies away from pianos as well
as moths.  This is taken care of by moth balls and mouse bait.

Also keep most children away from them.  If the child does not
respect the piano, as in being a student of piano, he/she is
likely to destroy or come close to destroying any old instrument
found in a garage.

D.L. Bullock    St. Louis
www.thepianoworld.com