SecondLife,
I finally got back here. Thanks for the picture of your wall design.
A good example of severe condensation is the interior of uninsulated tent walls that can sweat profusely from habitation on cool nights. Better insulated walls accumulate water molecules more slowly, but just as surely given time.
If you google vapor barrier install info in housing, you will probably run into recommendations to tightly seal the overlaps in polyethylene barriers since all vapor migration finds, and takes the path of least resistance. Vapor migration moves when air infiltration doesn't. If you desire, you might be able to seal your interior seams even better by simply adding a foil tape bridge, as metal foil has a very low vapor permeability. Single, dry water molecules are smaller and sneakier than air molecules like O2 and N2.
By humidifier I assume you meant dehumidifier, and that should also help immensely as a final resolution. Offhand, some folks here have installed passive air-to-air exchangers in campers for off-the-grid living. Ordinary venting is the most common method, but loses a bit more heat.
But really, just the foiled foam method you are using should prevent delamination concern in all but the very coldest temperatures anyway. The only physical process strong enough to damage riveting is actual ice build-up and ice swelling within the wall cavity, which does occur rapidly under some extreme conditions. In cold climates, most of us in rural areas have observed a frozen metal water bucket with the bottom bulged out from this powerful force. So some far-out camper environments with widely varying interior/exterior temperature differences need take this seriously into account. Perhaps an example is living aboard the International Space Station, which is nothing more than extreme camping (habitation). ;)
Painting: I did add some special vapor barrier paint to the interior surfaces of my own "pre-owned" stick home. Amazingly enough, there were no vapor barriers installed in ceilings in my city and most older exterior walls had no poly sheeting behind them yet either. FYI, most humidity accumulates near the ceiling because water vapor is lighter than ordinary air, so take extra care with ceilings. We have enlarged, remodeled and sealed our home over the years, but the original leaky house was built in the early 1950's, long before properly sealed windows were common.
Trivia: One interesting problem I once encountered, was a newly finished and heated garage that, by the following winter, my customer complained was starting to reveal all the drywall seams and nails. An investigation, showed that they had been warming their early carbureted auto with the overhead door just slightly open (to save heat). Consequently, all the wall studs had been collecting exhaust soot, dragged there by eagerly condensing moisture, and this made dark vertical lines every 16 inches, thus my customer thinking they were bad seams.
The reasoning behind this investigative science is that the wood is a much poorer insulator than the fiberglass bat used between studs. The colder studs then collected water vapor more quickly and the accompanying soot visually accentuated the differences in the insidious vapor migration process. Even more remarkable, each metal fastener (drywall screw) lost heat to the outside even faster than wood, making rather darker dots yet, nail dots distributed every few inches along the already carbon-shadowed studs. Part of the problem was that burning a gallon of gas produces more than a gallon of water vapor when combined with oxygen. Quite dirty water vapor, in this case of a '70's era auto.
I was able to demonstrate to my displeased customer that the soot easily wiped off the walls onto my finger. The agreed upon solution was to repaint and not warm up the auto in the closed garage which is dangerous anyway. What wasn't apparent was that the drywall fasteners and framing nails began to rust in the wetted wood under these conditions also. Lucky we nipped it in the bud.
Wes
