Let me start off my admitting that I am no expert on insulation but I have done a lot of research on this topic especially with metal buildings. Where you live makes a big difference.
Applying a little common sense to what I have learned, here is the basic problem. The metal is exposed to the outside air. If the outside air and the metal reach a temperature below your dew point, any humidity in the air will condense on the metal. In colder regions, this would mean that any humid air on the inside of the wall would condensate. Down here in the hot humid south, if the inside is kept cool with air conditioning, the humid air vapor would condensate on the outside.
In the south, with typical house construction, the vapor barrier would be on the outside of the walls. The idea is to prevent humid outside air from reaching the colder indoor air. In the north, it is opposite. You want to prevent warm moist indoor air from reaching the cold outside surfaces.
The key is to prevent as much moisture from reaching the cold metal. No moisture, no condensation. Air will travel through fiberglass insulation and I think this is where the general thought of not having fiberglass touch the metal comes from. That and the fact that many people with metal buildings with no insulation experience the rain effect as the water dripp\s off the ceiling in certain conditions. They naturally think that if there was fiberglass touching the metal, they would still have the rain. The key is to prevent as much moisture from reaching the metal.
I ran into the same situation building my shop and house. My initial plans were to use spray foam but the cost was much more than I planned. I was stuck with metal walls and no wrap. I decided on installing !" foil faced styrofoam sheets to the inside of the walls about one inch from the metal and then installing fiberglass batts.
Again, I am no expert.
