Can I get some help with moisture in the taillight housing?

If these backup lights aren't damaged, cracked and allowing water in to collect, they may have aged until the seal dried up and opened to allow water/moisture in. Each backup assembly would need to be removed to examine them after cleaning off dirt built up. One method is baking them in the oven (search youtube videos for how-to and temperature) to split open an assembly. Cleaning then using sealer like silicone caulking or other recommended sealer should prevent future moisture collection. A well placed small hole on top and bottom may allow moisture to vent.