Current limiting voltage regulator to power 12VDC fans
Those are 12V fans, so you can power them using just the 12V from the PowerStation. No extra components needed. No need for a voltage regulator.
A voltage regulator will lower the voltage, what you don't need. It does this by converting the extra voltage into heat, what you don't want.
You only need to add components if you want to run the fans at a lower speed. E.g. to lower power consumption.
$$\dfrac{18Ah}{0.08A} = 75\;hours$$
However the current the fans will use also depends on the voltage provided. So they will use more when the battery is full, and less when it is &quot;empty&quot; (11V).
Just be sure to not let them run for that long. As the manual states:

Check the battery voltage regularly when using the 12V outlet. Do not allow the battery voltage to drop below 11V before recharging or damage to the battery can occur.
The PSX2 will NOT automatically turn off power to the DC outlet. Continuing to use 12V DC appliances after the battery has been depleted can permanently damage the unit.