How can I cool a 2 x 3 ft metal enclosure located outdoors that has no holes or vents to a fixed temperature?

Cut a hole and mount a small enclosure cooler (alcohol vapor)

If cutting a hole is not an option then fabricate a heat sink and have the cooler blow on the heat sink.

use a simple house type thermostat for temperature control.

Use water cooling. If you have a source of water, that is actively cooled with a chiller, you can bring water into the enclosure with piping.

Inside, there would be an air-water heat exchanger. This transfers the heat of the internal air to the flowing cool water circuit.

Incidentally, you'll have enough information to calculate the internal heat created from your devices. By knowing the coolwater flow rate, the water temperature going in, and the temperature of the water circuit leaving the enclosure.

by just dumping cold water on the metal enclosure

with the assumption the enclosure is insulated\

a standard window style air unit with heat and cool capablities is ok