Does my little mango tree need to come inside if the temperature is
gonna drop briefly into the low 40's tonight?

Bob

Does my little mango tree need to come inside if the temperature is
gonna drop briefly into the low 40's tonight?

According to
http://davesgarden.com/guides/pf/go/2250/
you probably are OK as long as it isn't going to freeze.

The disclaimer is that a plant in a pot will be more susceptible than
one in the ground (because the cold air cools the soil), and cold
hardiness can vary based on things like whether it is sheltered from
the wind.