Closing In An Existing Metal Roof

I have an existing metal deck roof 14’x24’ with panels installed directly on 2x4 Perlins spaced 2ft on center that sit on 2x6 rafters also spaced 2ft on center (no sheathing or vapor barrier). The 6/12 metal roof attaches directly to the main structure roof that has a 10/12 pitch. I intend to close in the deck to make a living space. I want to insulate and close in the ceiling of the new room but am concerned about condensation on the underside of the panels. I have the option to create soffit vents but since the roof dead ends into the main roof I wont have full air flow through the soffit to the peak. Ive considered spray foam kits but want to avoid the extra cost if possible. What options do I have aside from removing the panels and adding sheathing and vapor barrier beneath the panels? Any help is greatly appreciated

Thank you for the reply. I understand that spray foaming the underside completely with closed cell foam would be the best choice. However, I’ve spoken with several foam manufacturers and the general consensus is that it would need to be sprayed at least 3.5” thick to constitute a true vapor barrier. Which in turn massively increases the DIY cost that is already high. Im trying to avoid this to stay in budget. Im leaning towards the idea of creating an air gap under the metal panels between the metal and foam insulation board tightly sealed/caulked beneath the perlins. Then, making soffit vents at the eave and venting from the sides at the top as there will be a closed in cavity from where the metal roof meets the existing roof. (See attached photos). After the foam board insulation I would then use 6-mil poly sheets on the complete under side. Ultimately then finishing the ceiling with tongue and groove pine boards over the plastic sheets. Do you foresee an issue with this method?