That is complete bunk about screws and threads!
Look around, almost ALL metal buildings these days utilize this construction.
They use self drilling TEK screws that are:
a. non corrosive
b. hardened steel, (they do drill
c. come with wide, water preventative washers
If you check and see you will probably find that your gas lines are attached to the frame with self drilling screws.
As for threads, as I said above, they use these to affix steel sheeting to the stringers that run horizontal on the building frame, certainly comparable to or even thinner than the steel in the frame assembly.
Almost all AC duct work utilize this construction on steel that is not even close to the thickness of the trailer frame.
All commercial buildings that utilize steel or tin studs use these screws.
Obviously, this practice is utilized and ACCEPTED by building codes and inspectors.
My 2 dollars worth!