A buddy who mostly dry camps like me made his own cheapie 'remote'.
He mounted a cheap digital thermostat right next to the fan and then put a NC relay between it and the fan (this also makes the load safe for the stat to handle), the stat is in series with the normal switch.
He sets the 'heat' to whatever temp he wants the fan to go off at as it cools down at night and when it hits that point the relay is energized, opens and shuts off the fan. The next morning as the temp rises back above the set point the fan automatically comes back on.