Install a metal roof vent, the square type with louvers on all 4 sides, well sealed where it contacts the roof decking..
One should do the trick but you also need to provide an inlet for the air to get in as the vent cannot suck from a vacuum, that would be best installed near the floor so that the vent can totally change the air out.
For a inlet vent I'd suggest the type with louvers as seen on the sides of house trailers and RV's. Again one should be sufficient and place it diagonally opposite of the roof vent location to get maximum cross flow. ( EG top rt front on roof and bottom left rear for inlet)
If you ever stood on the roof of a house near a vent you would sure feel the heat coming out of an attic, (heat and humid vapors go hand in hand)
Note that the turbine types have been proven much less efficient (and more troublesome) than the cupola types. They, by design, require a bearing to rotate which corrodes and freezes in cold situations.
RV type vents only work in one direction which is OK on an RV as you are pulling creating the wind (suction) but useless when static, in fact if the wind is the wrong way you would simply be pressurising the container and pressure would cause more condensation.