I put a cheap 12v LED puck with and a simple switch on the top of the hatch in my Astro Van. I think I paid like $20 total for the puck and switch. Best $20 mod ever. Wired it to my house battery with simple tiny wires. It isn't super bright or fancy but, honestly, it is frequently brighter than I, or my friends, actually want while camping. I can lower my hatch some to limit the "throw" of the light. But honestly, I'm learning that for cooking I prefer to use a small, rechargeable, goal zero latern with magnetic base instead. BUT having the rear light mounted and handy for many tasks (including packing the van) is invaluable.
So my advice is this. Keep it simple and don't go too bright. Having some light is nice but don't blind yourself, your friends or neighbors (if in a campground). You still gotta see the stars!