this is what i have at the moment for vent in bottom of van , its simply a house vent you would put in a brick , obviously this isnt going to stop the water coming in .... what have other people got ?
I used a couple of these, next to each other as gas drop vents. Also available in brown. This is what my van came with so I just replaced them with new when I refitted the interior.
Underneath the van there's a cover riveted over the holes to stop dirt and water getting in - a top hat section, half an inch deep.
"I'm a man of means, by no means....King of the Road!"