Finding air leaks when you cannot hear it?

Actually this is a two part process. Park in the pond but only up to the bottom of the cab. If it bubbles then its an outside air leak in the frame. If no bubbles roll up the windows but keep them open just enough so you can breathe. Then have billy bob fill the cab with the garden hose while your inside looking for bubble behind the dash. But you get 2 extra bonuses with this process. One it will show any potential places water can get in the cab up to the top of the doors as it will leak out and two it will rinse out the cab when you open the doors.

 

...and the insurance will cover the water damage done to the truck.

Sorry for that kind of irony. There is a multi page thread here from ozzydriver. He had and air leak which he couldn't track down and as far as I know he gave up on it.
Just search the forum or maybe another member can post a link to it.

Good luck finding it.