But for me, I would be considering sliding the roof felt strips between the roof metal and trusses. Then I would use no more than an R-19 standard fiberglass insulation or the high density batts at R-21. You will loose some of this insulation value due to compression towards the eaves of your roof. But insulation this thick still leaves some room for airflow. I would also install gable vents to ensure this airflow. Maybe even whirlybirds of the roof. I am not sure of the cfm all this would generate, but it would be critical to have sufficient air flow to remove moisture that will build up in this roof. I would also use non-faced insulation (no paper layer) and depend on sheet vapor barrier attached to the bottom of the trusses before adding the ceiling panels. The only thing I have seen factories install is 4mil poly, which is readily available in bulk at your local home store. I would not know if current new manufactured homes are using a home wrap instead of sheet poly. Again, I do not live in an area where condensation is a major problem and I have not worked on many 2004 or later homes. I usually get the jalopies.
These are my recommendations because this is how I see the homes are built in my area. There are always trade-offs. I don't think any system is perfect in all weather conditions.