Well I'm not sure that all slide seals actually fill with air. Country Coach seals don't. If you have a seal come loose, you will have an air leak even when the slide is in. The seal needs to be lubricated to prevent it from hanging up and breaking loose, causing a leak. I used white graphite on my CC, but you need to see what HWH recommends as a seal lub.
I could actually start and drive my coach with the slide out which I found real strange. It was handy a few times to move a few feet without bringing the slide in.
Loc uses a wide load banner while driving the DS Millennium down the Interstate with both slides out.