The Tailor trader offers a service to fireproof any item made of cloth.
(Android version 1.3.4) The Tailor doesn't fireproof the Certus bow - and (my guess) neither any other wooden weapon since they are not cloth. If so, the only way to fireproof them is by pouring a potion of fireproofing into it. Will also reset burn statuses, if any - "(You weapon) looks like new!".