I thought about that also but you'd just about have to be completely under water before the water droplets could flow/move uphill to get into the tube. I mean water flows downhill. I guess as a precaution you could stick a small slotted vent (louvered) so that air can still flow through but with the vertical slots slanting down (like an AC vent), then there would no way for water droplet to climb into the tube.I think it's a cool idea. My vents are blocked off so any smells wouldn't be an issue. Besides any vapors coming from the engine compartment would be hot and rise straight up through the cowl slots so I don't see an issue. Going down the road you'll basically have RAM induction because the factory put the cowl slot where the highest pressure collects as you go down the road. That's why you get such good flow through when you open the vents in the car.
Treblig
