I minimized this by making sure that no hot wires were spliced inside the hood, and the switches inside the hood are all switching the ground wire. Also, I put on a little control panel onto the hood so that you can turn the fans on and off, override the timer, and turn off banks of lights. It's a really easy thing to do and really convenient. I recommend this too. If you decide to put fans in your hood, don't be stupid like I was and base your purchasing decision solely on the size and voltage requirements.
Varnish smells bad.
I've had the windows open and the fans blaring, hoping to put a stop to it, but the odor continues. I saw some advice posted here about whether fans should blow into the aquarium or out of it. Someone suggested blowing air directly onto the water would increase evaporation. I fixed mine to blow air out - I figure the primary mission here isn't to cool the tank by evaporation, but rather to remove the heat from the lights. I've copied that design.