Accorion Seals
 

Was having an interesting discussion about the seal and the cab aperture (opening) relation to the box aperture.
The motorhome spends 99% of its time parked. The function of the seal is to join two compartments that at times have a dynamic relationship (they move with respect to one another).
My measurements show our cab when aired up is 1.75" higher than when deflated.
Ignoring side to side movement for a moment, most of the cab movement when aired up is in the down direction.
The question is, would you set the two apertures aligned with each other at rest deflated or aired up?
Keep in mind the purpose is to seal & join two compartments, while underway there would be minimal traffic between the to compartments, most traffic would be when parked and deflated.
Now, mechanics of this would say when underway you'd want as close to a neutral alignment to allow for the greatest movement between the two, yet when parked (all weather conditions) you would not want it to be under stress.
Further consideration is this passage way is going to be small; about 30 wide by 59 tall so misalignment while parked means this would be further reduced in height when it would get most of its use. Other side of the coin is while underway you wouldn't want a smaller tunnel either?
In the end it really comes down to aesthetics; I'd prefer it were lined up instead of like a train tunnel started from both ends at once and not meeting in the middle.

Maybe I am not reading the problem correctly, but why would the cab be in a different position while parked than while driving? Is there some need to release the air once you are parked? My experience with air bags and air controls (not on a cab air bag) is that properly installed leak free, they really don't lose air over time so the cab should stay right where you left it while driving. So, making that assumption just leave it aired up and set the opening accordingly and there should be no misalignment issues under other conditions.

When we did lowrider air suspensions here in our shop, the bags would stay aired up indefinitely assuming the correct leak free installation. Same story on the air bags on my trailer saver air ride hitch, it has 5000# of trailer pin weight sitting on it and it never loses any air at all, sitting for weeks at a time between trips.

seal
 

I made the opening in the motorhome match the cab while it is aired up. My Peterbilt does not leak down at all. I can reach in between the cab and motorhome and release air but I just leave it up.

Thanks Ken, nice work.