It wouldn't be anymore difficult to waterproof a mod than it is to waterproof a radio or a camera. BUT, then It wouldn't be vented. It's impossible to waterproof an atomizer, so the PV wouldn't work anyway.
This is what I use when out in the wild:
A couple of years back it fell out of my duck blind, and spent a week in the mud at the bottom of Ogden bay. (my dog found it) I rinsed it off, put a new battery in it, and a new atomizer, and vaped away.
Been vaping away on it this morning too.
So don't worry about being waterproof, worry about being able to fix it if it does get wet.