I used 'Astrofoil' throughout our new House, just under the Drywall, as the Vapor Barrier and as an Infrared [IR] 'bounce' or reflector. The Company also sells special Tape to seal seams, since Tape like Duct Tape has adhesive that will not hold up over time.
The proper deployment is to install Astrofoil [or identical 'Reflectix'] immediately under the interior surface. In a CT, this would be just under the Luan; Plywood; Vinyl, etc.. Moisture/Humidity precipitates out when warm interior Air meets colder external surfaces [the metal CT Skin]. Astrofoil blocking that warm Air, by being placed on the interior side of Foam Insulation [or any other Insulation] is a good thing. It also helps some Insulations work 'better' by keeping moisture out of them by keeping the warm interior Air/cold exterior Air 'interface' out of the Insulation. On that side of the Insulation, the temperature differential is not so great, so condensation creation is not so pronounced.
Astrofoil is thought to provide up to an R-7-equivalent Insulation value by the Infrared 'bounce' effect, and by the single Air bubble insulating characteristic. There is also thicker Astrofoil that has 2 independent Air bubble layers [instead of 1], and thus a higher overall Insulation rating.
There's another Astrofoil Product without Air bubbles that has moisture ventilation holes in it. As specified, I used it on top of our Roof Trusses, just under the Roof Sheathing. It 'bounces' Heat out of the Attic, keeping it ~30 degrees cooler in the Summer, and thus lightening the Cooling load on the occupied Interior space. Another intended use is to lay it in an Attic over existing Insulation where it provides additional R Value as a retrofit application.
A scrap of either material works very well under a Trailer Bottom Sheet as an electricity-free Heater that uses only Body Heat. I've used it Boondocking by hanging a scrap vertically and sitting up against it on cold, sunny mornings. It creates a nice micro-environment of warmth.
There's all sorts of 'Voodoo' beliefs posted on Forums regarding humidity and Insulation. Some 'Pundit's' have even proclaimed Insulation is something to be avoided as a 'shoot yourself in the Foot' way to avoid humidity-related issues. In any small volume with humidity, like a House Bathroom, the answer is uniform: ventilate the volume. This is also true in a Trailer, with Cooking or Showering humidity [or simply humid Weather].
The bottom line is that an insulated Trailer space is more comfortable and needs less external energy - Propane or Electricity - to keep it comfortable, and to extend the Camping/use Season. Concerns over Carbon Monoxide buildup or Propane leaks are best addressed with well-maintained Detectors, just as in a House.
Astrofoil Website