I am attempting to create a fog machine tornado right on top of my case, the heatsink will be the main part exposed to the fog machine/air mini tornado. Since fog machines are water based, will using conformal coating protect my parts from damage?
LOL - seems like retro '60s psychedelic, but I'd be careful about spraying the insides of the case with any coating. I think the circuit board manufacturers already coat the boards, and the copper-based heatsinks can have a coating applied to them to prevent them from turning green, but too much and they lose some effectiveness in heat transfer and hence not able to cool as well. And unless you really coat the inside of the case, I'd worry about condensation shorting out something, esp. the backside of the mobo where water can drip down without you seeing it.
Also you might consider a custom-built or modified case with air intake ducting to take in cool air far from the fog effects area. You could run plastic dryer vent duct from the bottom of the case through whatever it sits on to outside or another room. Or go with a completely sealed case with water cooling or oil immersion.