To create, edit or delete trailer groups, use the command resource/update_trailers_group:

svc=resource/update_trailers_group&params={"itemId":<long>,
					   "id":<long>,
					   "callMode":<text>,
					   "n":<text>,
					   "d":<text>,
					   "drs":[<uint>],
					   "f":<uint>}

On create and edit:

[
	<long>,		/* group ID */
	{
		"id":<long>,	/* group ID */
		"n":<text>,	/* name */
		"d":<text>,	/* description */
		"drs":[<uint>]	/* array of trailers IDs */
	}
]

On delete:

[
	<long>,		/* group ID */
	null
]