It's not fancy at all but I used a cheap 18$ light from amazon, in "smoke" color. I like the look, I'm sure you can shop around and find something nicer or your style. It's been installed for 3 years now and hasn't leaked a drip. It comes with a neoprene gasket. I also ran a tiny bead of clear 100% silicone from the hardware store around it just for security. FYI, if you get the same exact model as mine with the side white leds you will have to run a wire because our trucks dont have reverse lights on the 3rd brake light as far as I know, maybe some models? I used mine as bed lights..... not very bright tho. More for ambient light when camping or something.
Do be sure it's not your rear window though. The only reason I replaced mine originally was chasing a dampness in my headliner. It ended up being the rear window seal and the water wicking up the headliner. I recently pulled the light off to check for any leaks when replacing my rear window seal and it was still bone dry, after 3 years.
Cheapy amazon LED light with seal