I would consider making a custom magnetic illuminated license plate holder consisting of an aluminum plate serving as the license plate backing with an appropriately powerful magnetic strip epoxied to the back, an aftermarket led license plate light kit which replaces the upper license plate screws, and a small rechargeable battery pack serving as power. You would wire in a waterproof microswitch to turn the lights off and on.

Trophy Truck LED Stainless Steel License Plate Lights | eBay