I’m looking at 2nd Ave N in Nashville on Google Maps street view now - another thought occurred to me - what if the (I know, just like in the movies) RV had been modified and had an access door on the bottom. Suppose also, that the RV parked on top of a manhole that allowed access to either the communications tunnel or the electric supply tunnel belonging to the local power company, Nashville Electric Service.
Now, suppose that the inhabitant of the RV got into the tunnel and unloaded a bunch of explosives at/near the location where the comm cables enter the AT&T building. Something big blew the covers off the underground vault alongside the building.
That would not explain the gunfire that witnesses heard though. Unless that was an unrelated incident.
One other thing I noticed from the satellite view - the building attached to this one, directly on the corner of 2nd and Church appears to have a pair of backup generators on the roof. That would stand to reason, being that it is a communications hub.
I will consider the things you stated. But in answer to the gunfire comment, Someone said they thought it might have been at the begging of the recording. Useful to keep others at arms length, so to speak.
Ps. got to look for a manhole opening after the blast occurred.