Both mesh and purlins reduce summertime heat penetration to the interior somewhat but i believe the significant advantage of the more effective ventilation gap provided by purlins is the reduction of the summertime temperature of the metal roofing itself.
Roof repair gap in tin.
Cover the base coat with a piece of glass membrane fabric.
I am not a professional roofer but.
Apply uniform layer of metal roofing base coat 6 inches each way of the gap at the overlap with a paintbrush.
Fill small nail holes with silicone caulk or roof cement.
Repairing a metal roof seam with turbo poly seal is simple and it is a do it yourself p.
Typically this system is installed over a structural metal roof system where the existing roof system becomes the metal deck for the new roof system.
Smaller nail holes will be permanently fixed by this method standard roofing nails would be either 3 8 inch or 1 2 inch making a hole.