I plan to install 5-V steel roofing on a carport, covering existing asphalt roll-type roofing. I could use any advice on the right way to do this. I have the nails with washers, but I was told to pre-drill holes for them, and also to nail at the top of the "V". How do I drill at the point of the "V"? Also, is it necessary to caulk seams? The roof is a slow pitch, but not flat. Probably about 1 in 12. I could find only 12 ft. long sections at local building centers, and must use two per section on my 21ft. deep carport. I plan to caulk the overlap. Any other tips I should be aware of before I start the job?