Some neighbors of mine have an old door that has been left out in their
yard for a few years. The door is solid hardwood, and appears to be
quite old (it comes from a house that was built in the 1880s). Despite
having endured rain and snow, it appears to be in good shape. I cannot
see any signs of mold, rot, or splitting. The joints are tight and the
corners are square.

Rather than watch a perfectly good door go to waste, I would like to
use it as an exterior door into my basement. However, I want to make
sure I prepare it properly. My plan was to sand, prime, and paint it.
Can anyone recommend further measures to do make sure it remains in
good condition?

Thanks,
Joseph