Would this compact auto top off system work well?>

[Rippin]

I just use a small water pump or peristaltic pump in a pail of fresh water hooked up to a digital timer that can turn on/off in 1 minute increments. Once you've determined the amount of evaporation, you can set how much and how frequently the pump turns on. This assumes that the amount of evaporation is constant throughout the year. Also, if there is a power outage, the digital timers have a back-up battery, so it won't stop topping up.