Best mounting system for panels on new metal roof

[J.P.M.]

Well, if the roofing companies trust a little 1/2 dia seal on their screws, and the engine makers trust compression seals on cylinder heads, I have no trouble trusting a 3" sq L-foot on a roof.

Compression seals on engines are a different application, but I'd also suggest they fail on occasion. I've designed various types of compression seals for many types of pressure vessel applications. interesting tech.

Keeping a joint dry in a weather application by flashing for example, is a superior method of leak prevention over relying on sealing methods that can dry/change dimension/deteriorate over time, but sealing screws is certainly a cheaper method. To the extent you may me correct, I believe cost may have something to do with their trust.