I am making woodwn whiskey bottles. Looking for something safe to seal the inside of bottle.

Even wooden Whiskey Barrels are not completely sealed. They breath.

The only suggestion I could make is a plastic, or glass, insert on the whiskey container. I don't know of any sealer that is not only safe for food or drink, but makes the wood impenetrable. I'm a woodworker, but I have to admit, I don't make items that are used with food or drink. The one thing I do know is wood, and liquids and wood, they don't mix.

I also have to say, I don't know whiskey, but I'm fairly sure that whiskey and glass do mix. Have you considered a glass insert?