As the van leans, I would guess it generates some serious pressure on the
outside bag.  The inside bag would expand and drop pressure.  Pressure
would transfer to inside bag, lifting inside spring?  It would take some
sustained cornering to do this--typical back and forth probably not a
problem?
I have mine separate.  It would be interesting to see if someone had
individual gauges on theirs what the pressure swings might be during
cornering.

                                                   Jay