As Roy stated, making use of the die cast tender body as antenna works great, as I have done with MTH and Weaver brass tenders. Also, making an antenna with use of a "bell pull" insulated wire is an option worth looking into and giving a try, as John said, also. Along with placement of an antenna under a plastic tender shell, to increase the reception, you can make use of the tender's wire made handrails, even making your own to use as antenna and add detail to the tender.
Jesse TCA 12-68275