Mobile Home Metal Roofing over shingles

4 Questions.

1. I have a 1988 double wild mobile home with a 2" - 12" pitch and would like to add metal roof over shingles. The manufacture paper work of the metal roofing panels has a min of 2-1/2" pitch. I asked the sales person if ok, they said I just have to add sealant on all the laps. Is this ok?
2. I have two vents on both ends at the top under side of the mobile home and no vent at the ridge. Can a mobile home with 2" on 12" pitch have a vent at the ridge or is it a bad idea?
3. I'm putting on underlayment, 1 x 4 battens/purlins, foam board(The blue foam board from Lowes) and vertical seam metal panels 26 ga. should the underlayment go under or on top of the foam board and battens?
4. Should the metal roof be able to vent air threw the ridges of the metal panels? The installation show foam going under the metal panels at the eave and no air can pass threw to the ridge is this ok?

Thanks,
Ron

Any pictures of the home? If you are sealing up the roof design and adding foam, you may not require any venting of the roof at that point.

Hi, I have a 16x80 mobile home with a 3 12 pitch shingle roof. The shingles are still in decent shape so I'm going with metal over the existing shingles; I plan to install the metal sheets over the cedar planking. Should I use underlay before fastening the planks to the existing roof? My concern is condensation.

Correction; the roof is 2 12 pitch not 3 12.