i bought cubes from amazon similar to the ones above, but without the in bumper mounting option. i put a pair on the back of my land cruiser and my sons bronco. they have been surprisingly useful. i bought bulk wire from home depot and bought some custom switches from
https://otrattw.net . i used waterproof hella brand relays as well.
funny story, my son was driving and had accidentally turned on his rear lights. he got pulled over and got a warning. the officer was more interested in where he got the lights as he wanted some for his truck.