RE: Help - Water in the hole!
Are you sure you don't still have some water or moisture in your board?
By placing the vent facing down, you do indeed get the effects of gravity to drain the liquid water out of your board, but any water that turns to vapor as your board warms up goes UP into the foam as vapor rises and is not affected nearly as much by gravity as the liquid form.
The principle (using the vent plug up scenario) is that the water turns to vapor as the board heats and the expanding air inside the board "pushes" the water and water vapor to the surface where you can "wick it out" with a paper towel.
I think that placing the vent plug down would work OK at nite and when the board is cooling to allow any liquid to drain out, but for using
mild heating to push the water and vapor out, during the day, it seems having the vent plug up might be more effective.
You are correct, if you have a ding, and want the water to drain from the ding, then putting the ding at the "low point" is best.
After all liquid has drained off, then put the ding at the high point and alow your board to warm in the van.
Hope this helps,