In the British Aerial Corps, combat dragons are fitted with several types of harnesses, including a light duty harness, travelling harness, and heavy combat harness. The harnesses consists of thick leather straps held together with large metal rings. On the belly of the dragon, the harness consists of a net (referred to, unsurprisingly, as the 'belly-netting') in which bombs, gunpowder, and some of the crew are kept.
The Crew travels from place to place upon the back of the dragon by means of a series of carabiner hooks and rings: the crew member would unclip the hook (attached to their belt) from the ring, move foreward (or backwards, sideways, etc...), and re-clip the carabiner the carabiner when they have reached their location. If moving a relativlely long distance across the dragon, you would unclip and re-clip several times. While this method is rather slow and tedious, you remain attached to the dragon's harness most all of the time, which is extremely important should the dragon perform a manuever such as a roll. Such a manuever would result in many of the crew falling off the back of the dragon if they were not held on by their carabiners.
Harness fitting and rigging is the responsibility of the dragon's ground crew, with the main responsibility falling upon the harness-tender.