A platform lift trailer includes a chassis to which a lift device is mounted. The chassis is configured to be coupled to a standard motor vehicle trailer hitch or the like using a coupler. Some embodiments of the coupler provide protection against larges torsional forces applied between a motor vehicle and coupled trailer when they are angularly displaced relative to one another. One or more ground-engaging wheel assemblies are mounted to the chassis to assist in supporting the weight of the lift and any cargo thereon. The platform lift trailer is highly adaptable so that a wide variety of lifts can be mounted to the platform lift trailer and thus to smaller motor vehicles. Adaptation of mobility lifts and the like to a larger array of motor vehicles is therefore possible. One or more embodiments of a trailer coupler use torque-limiting apparatus so that vertical angular displacements of a motor vehicle and a coupled trailer do not apply large forces directly between the motor vehicle and the trailer. Instead, the coupler torque-limiting structure limits such forces using a biasing means such as a spring or the like to accommodate or limit torsional forces applied between the motor vehicle and the trailer. The biasing means also can limit the maximum angular displacement allowed between the motor vehicle and coupled trailer.