A good cleaning regime and ACF50 should be fine. My 125 was 6 years old and Chinese as is my 250 (so worse metal than your CBF) and neither have had any real rust issues just from elbow grease and ACF50/WD40.
Or is your frame massively peeling and rusted? If it is and the bike is under warranty I'd contact the dealer/Honda as if it's rotting before it should due to poor workmanship it's on them to sort it out (powder coat). Even if the warranty has expired I'd send a long letter to Honda asking why they think it's ok to put their name to an Indian made bike that can't handle UK weather.
