A trailer has no spring brakes and must be left parked. According to the AAMVA manual, what should the driver do in addition to setting the parking brakes?

AAMVA CDL Manual, Section 6.2.1 "Trailer Hand Valve," p. 6-4

Spring brakes normally guarantee a parked trailer stays put even if air pressure is lost. Without them, air leakage alone can let the trailer roll, so wheel chocks are the mechanical backstop the manual requires.