New roof using corregated metal sheets

[flint]

I have a few questions regarding installing new roof: First Im a little confused regarding order of installation of materials for new metal roof according to Mobile Home Manual. Instructions indicate to put down fan-fold insulation first then furring strips and then the metal. I talked to Metal Distributer Sales person and they were familiar with installing roof on MH with their metal. They said the furring strips go first and then the fan fold goes on top of furring strips??

Secondly I cannot find the fanfold in 1/2 inch. Checked everywhere in my area and beyond and 3/8 inch is best I can find. I would really like to use the fan fold instead of 4 x 8 sheets so I can buy and transport myself and seems it would be much easier to work with. I'm assuming the 1/2 inch is definetly better but just wanted your thoughts on the 3/8 inch stuff.

Lastly I'm getting a little concerned about the method I was going to use to reroof my covered porch. I was all set to tear off old rolled roof and lay down 30lb felt over bare plywood and then furring strips and then the metal..(this was advice from metal distributer also). However, I checked the drop down distance between trailer roof and porch roof is only between 2 and 2 1/2 inches. With the added height to the porch roof, Im afraid I will not get a good seal between trailer and porch roof and have major leaking issues. I've been thinking about a contractor I ran into a while back who was reroofing a porch roof on a house. The roof was pretty close to being flat (same as mine) and he layed Titatanium UDL Underlament first and then a rolled roof. I'm wondered if this might be better than the metal.

Please help!