Ag metal on mobile home roof

I would not mind seeing some sort of space between the metal and the roof deck. I am concerned that you could drop the roof deck temperature enough to cause condensation that didn't occur before inside the attic. Battens would help create that space ... or you could also use a breathable synthetic underlayment (Vent3 is one I like for its high PERM rating) and then an entangled mesh product ... this allows moisture to drive out and the airspace created by the entangled mesh helps prevent dropping the roof deck temperature too low and also gives a space for moisture that is driving out.

My suggestion is breathable underlayment over the decking followed by battens and the metal ... or you could use an entangled mesh product instead of battens. Thanks!

My suggestion is breathable underlayment over the decking followed by battens and the metal ... OR you could use an entangled mesh product such as Dry-Tech instead of battens and install the metal panels over it. Now, you have also mentioned the possibility of "cross battens" or similar. This would be placing vertical battens over the decking and underlayment as "sleepers" over the rafters and then your horizontal battens over those. That is certainly a nice idea and would enhance things by allowing air flow up the decking beneath the horizontal battens. You also could probably use spacers as you suggested. All this said, you need to also make sure that what you're doing meets local building codes.

I think you will have a tough time finding any breathable in stock at a local big box or lumberyard. I am sorry. They just aren't used very often. I generally rarely see a need for them except in situations where traditional ventilation is extremely limited. Breathable underlayment by the way are not a "cure-all" but they can be helpful toward creating a system that works. GAF has a product called DeckArmor that is probably most likely to be in stock. It has a breathability rating of 16 PERMS. Vent3 is made in the UK and stocked in OH by RoofAquaGuard ... with a much higher PERM rating. In the interest of transparency, I will say that RoofAquaGuard is a part of the company I work for. I do see that Menards offers a product called Hydra, also 16 PERMS. A company called Proctor from the UK was perhaps the originator of these types of products but I doubt you will find it in stock anyplace.