In the past the ARRL has often had a physical pullout section in QST with all the rules for field day. Not this year. I am assuming it is part of their austerity measures. I could download the pdf file from ARRL’s website, but with whatever kind of cyber troubles the ARRL HQ is undergoing, the download link is broken. This is also true for Log of the World (LoTW) as well as the QST archive.
The ARRL does have the rules online and I pulled the sections that will apply to my mobile operation:
(Class C) Mobile: Stations in vehicles capable of operating while in motion and normally operated in this manner. This includes maritime and aeronautical mobile. If the Class C station is being powered from a car battery or alternator, it qualifies for emergency power but does not qualify for the multiplier of 5, as the alternator/battery system constitutes a motor-driven generating system.
Stations in ARRL / RAC sections will exchange their Field Day operating Class and ARRL / RAC section. Example: a three transmitter Class A station in Connecticut which also has a GOTA station and the extra VHF station would send “3A CT” on CW or Digital, or “3 Alpha Connecticut” on Phone.