I'm amazed that they permit the bike with so much fuel on board since it can potentially leak and fill hold with flammable fumes. Some airlines will not even permit a used camping stove if it uses liquid fuel, even if fuel canister is empty.

Vehicles & camping stoves are two entirely different things. Vehicles are designed so that the fuel will not leak and fumes will not leak, and it is not possible for a vehicle to be loaded in any way other than right side up. It's also not possible for a properly secured vehicle to overturn in flight.

Camping stoves are not designed with particular attention paid to leak prevention or fume release, and they could be loaded upside down or sideways, and could overturn in flight. Plus, the nature of the fuel is different - camping fuel is generally more volatile than auto fuel.

Personally, I would not bet on it. Once you start securing cargo to the outside of the moto, you begin to get into a grey area. I doubt that any cargo acceptance agent would refuse a helmet hanging off of a helmet hook on the side of the bike, but a bag full of stuff strapped to the rear seat becomes a judgement call on the part of the cargo acceptance agent that would be difficult to protest against.

Give it a try. If your bag gets refused, you can just check the same bag in as checked luggage when you board the aircraft with your passenger ticket. Personally, I think you would enhance your chances of success if the bag only contained one or two bulky items (for example, your riding suit and your helmet). But, it's 'iffy' - it all depends on how the agent interprets policy.

Michael