I've had Fantastic fans in all three of my MHs. I would hard wire it so you can use it at night. The Fantastic has an option that detects rain and closes the hatch. Also a thermostat so it can turn off when the temperature drops at night.
That said, running the wires to it may not be that easy. Are there wires near your hatch for something else? In that case if you can run the "always on" wire through the roof you may be able to ground it elsewhere. If there is no always on (my lights have an embedded switch so thay have an "always on" wire, at least as long as the disconnect switch is "on") then running from an existing light may be a better option. You may be able to wire a switch into the light itself.