With all due respect, and having consulted the Wise Lady from Philadelphia, the cost of putting down 6 mil poly as a ground vapor barrier under a mobile home costs less than $60. U.S. If I were selling a home and if that were the only concern raised by a buyer I would leap into...
Once you understand that all foundations are full of water vapor you start to realize that the primary objective of the vapor barrier is stopping moisture from the foundation from entering into the finished framing where it might lead to mold. As you can see in the adjacent sketch the basement...
I don't have a perm rating yet but 6 mil polyethylene has a perm rating of about 0.06 - very low. That would explain why, if I guess right, the product is micro-perforated to let it breathe moisture vapor out while keeping actual water out. OPINION: I prefer the non-plastic house...