Bill, I'll have a similar light bar on the hatch of the wider than 80" trailer I'm building. I've thought about the best place to locate it. Similar to yours the easiest place to attach it would be right between the tail lights. It would be aimed correctly but probably not as noticeably conspicuous as it could be. To make it really conspicuous I'm contemplating attaching it to the hatch lid a foot or more higher than the tail lights by using an angled and epoxied wood block behind it to aim it correctly to the rear. The light bar I have also has a 3rd brake light function.
Perhaps, an alternative way for you to attach the light bar so it's even more conspicuous would be attach the light bar higher up on the galley hatch. You could make a support from a block of wood cut at an angle. Seal the wood well and paint it to match your TD.