In the south, anything kept in the dark is prone to mold. BLO has been a stock finish of choice for firearms for many years. When I open my gun safe I can just by sight tell you which ones have BLO finishes. They are often covered in white fuzz. The ones I finished with Tung are not.
Related to out doors.. I have several pieces of furniture that are a couple years old and treated with Tung oil that are holding up well considering they have endured two significant hurricanes. Poly would already be suffering from the UV. Will upload some photos tomorrow.