Are there and kidney diseases that cause chronically low potassium? even with normal bun and creatine?

Yes. : They lesions or diseases often are accompanied by high bp. There are kidney tubule defects or hormonal disturbances related to the adrenal gland function that can cause low potassium yet lab testing show normal kidney function in terms of clearance. Also medications and herbal supplements (including even exotic type of tea, licorice, or some tobaccos) can cause potassium disturbances.

Low potassium: Yes. Bartters Syndrome, Gitelmans Syndrome are two genetic kidney diseases with low potassium.