Awesome. Glad to see a part two. Thanks for sharing.

It would be a good idea to spray the foam insulation with a pest retardant. Mice love to chew tunnels and little homes in it.

A few things.... The reason your 2x8's had moisture on them is because they were cold (obviously) and the water vapor inside the warm building condensed when it hit the cold pine. Soft wood has about a 1.5 R value per inch of thickness. So you're only talking about like an R-2.5 on a 2x8 (which is why it was so cold). Using that closed-cell sheet to cover the 2x8, stops the warm air/moisture from reaching it, so it should stay dry. As long as the air from inside can't reach the purlins, you shouldn't have any moisture issue. I also believe you're wrong about the air gap between the steel and the insulation. You insulated the ceiling instead of the underside of the roof deck, which means I'm assuming you have a ridge vent or gable/soffit vents? Air is only an insulator if it is not moving. So, if you have moving air between the steel and insulation, it will NOT act as insulator. Actually it'll be worse, because that moving air will have moisture in it, and if it changes temp while moving through your walls, it could create condensation on the steel. Having the insulation up against the steel leaves less room for air, which means less chances of moisture between steel/insulation.

“We didn’t want a poly vapor barrier” why don’t you want to go into it? It should have prevented the frost on the inside of the exterior purlins during the large temp difference day(s). Also it definitely looks like your 2x6 purlins are 2x6 purlins and you corrected to 2x8. I’ve never seen a 2x8 purlin even on 20’ tall/commercial barns. Did inspection say the tape is not needed to pass code for vapor barrier? I’d think so as closed cell spray foam alone is considered a vapor barrier.