galvanized metal against PT lumber

Good choice using metal roofing. In Port Charlotte and Punta gorda, the metal roofs did the best. The older asphalt shingles, with staples blew off, and the rain went through most roofs, soaked the cieling/insulation and it came crashing down. Now there are thousands of homes with mould and mildew all over the inside.

So even though there may have been many homes without structural damage, the rain coming in after the shingles blew off is what did the real damage.

In one of the "higher end" portions of Punta Gorda they had a local ordinance that required tile roofing because its stylish.

But Charley liked the "stylish" tiles too, making great missles flying all over the place and bombing everyone with shrapnel.
This is a picture of a friends house after Charley.

The Metal building folks, and Home Depot, sell a screw with a rubber seal on the head. For wood purlins, it is pointed (no metal puncturing drill bit on the end) and drives with a 1/4 " bit. Some of these are painted, some galvanized, and they are made of high tensile strength material which would resist a chemical attack, much better than soft steel that hammer driven fastners are made from.

Good luck and hope you the best. Hope those "girls" lined up across the Atlantic to E. Coast of Africa leave you alone.

Mark