The fan should help, but then you're relying on the doorjambs and windows and furnace intake to replace the air that is drawn out.
75%-80% humidity is going to end up being a real problem for you. When it starts to get cold outside you'll see what I mean - the outside walls and windows will get a heavy condensation form, especially at night, and this in turn causes things like mildew and mold. In the summer it's not so bad, in fact you may even get to like the humidity - but yeah ultimately 75% is way too much for our climate.
I know this because humidity has been a problem I've been battling for years with my tanks. In my old house, the outside walls were 2x4 and this wasn't adequate insulation against the temperature differentials. So I built a new house using post-2000 building code rules and guess what, now houses are so air-tight in their quest to be more energy-efficient, that it's the same problem all over again (just due to a different reason) - the house just doesn't have enough air turnover to shed the excessive humidity.
Anyhow, the fan should work. It's not the best solution for our climate but it will vent the wet air out, which is what you want.
The ultimate solution is to use a HRV ("Heat Recovery Ventilator") instead of an exhaust fan. The concept is basically the same (ie. venting air to the outside) but with two important details: 1) The air that is vented outside is replaced by air from the outside, thus removing the "air deficit" that a fan alone would create, and 2) It uses an heat exchanger to use the outgoing air to preheat the incoming air (which is important when it's -40 outside). They recover something like 85% of the heat of the outgoing air, which is good when it comes time to look at your monthly heating bills.
Anyhow hope this info helps. Definitely do a fan or something, 460 gallons evaporating into your house will have an adverse effect.