To get list of binded trailers, use the command resource/get_unit_trailers:

svc=resource/get_unit_trailers&params={"unitId":<long>}

{
    <text>:[	/* resource ID */
	{
	    "id":<text>,	/* trailer ID*/
	    "nm":<text>,	/* trailer name*/
	}, ...
    ], ...
}