I find it very hard to accept that the local PoCo has no standards for a service mast.
I'd use a minimum of 2" Rigid. The weatherhead should be at least 18" above the roofline. If more than 30" above the roof, additional support is needed.
The mast is typically supported in three places. First, there are two places on the wall, where the mast is attached to "thin" strut. Strut is used, so that the anchoring lag bolts can be sunk into the framing - not just the siding.
The third support is where the mast pierces the eave; the roof itself helps hold it in place.
As for the "mechanic" who relied upon drywall screws: I recently replaced such an installation. All it took was for the roofing crew to remove the old roof, and the "service" fell into the yard. As you might guess, there were lots of sparks, and the "all in one" panel was trashed.
