I have seen them built in to the rear engine hood but a few non intrusive options are...
If your car is converted to neg ground you can put LED red bulbs into your back up lights and wire into turn signals for more light power.
I have avalable RED back up look a like lens.
you can change the lower red reflectors into small LED trailer light marker ass.
there is a licence plate chrome cover that has the 3ed light built into it. but to make it work on brake only you would have to run a wire up to the brake light swith on master cyl.
If you change your std turn signals to LED you have to use a LED FLASHER or they will not flash.
Driving my Fiberglass car dowen here in Florida I feal much better knowing they can see my very bright LED tail lights, there is a picture of them on the fiberglass amphicar feed I up posted yesterday. I also put trailer LED under them that come on only with brakeing.