Inside? Your going to try to snap apart a plastic housing so you can apply teflon tape? Most rear lights I've seen do not have any screws for taking the unit apart, that means you will have to snap the plastic clam shell open which will more then likely damage the light. Try tefloning that after you've broke it. The only place you could use teflon is the battery compartment, but since your not going to be screwing the lid on but rather snapping it on, how are you going to keep the tape in place? Teflon tape is designed for threaded applications to keep liquids from seeping past the threads and requires a male and female thread. That's why I use tape...get it?