Fiery Cross is probably the best option. Apparently it lies outside of anyone's 200km EEZ, so is politically the best option as it's in a "neutral" zone.
Come to think of it, would it be in China's interest to offer up Fiery Cross as a permanent base for joint patrols with various littoral nations in the South China Seas?
>>> Direct US-China conflict scenario deleted. It is against SD rules <<<{/b]
Let me rephrase it then.
China is the world's largest trading nation and sits in the geographical centre of Asia.
If you look at the trade flows, the Asian trade network is actually China-centric, with most of China's trade flowing through the SCS and China dominating the trade flows in the SCS.
Therefore there are literally no scenarios where China would EVER want to restrict commercial freedom of navigation in the SCS, no matter what happens. The coastal littoral nations of the SCS are in the same situation, as they are even more dependent on freedom of shipping in the SCS.
However, various other nations from outside the SCS do have an interest in shutting down trade in the SCS in various conflict scenarios.
If there was a joint base at Fiery Cross between China and various other SCS nations - this would help protect freedom of commercial navigation in the SCS.
So in order to successfully shut down trade in the SCS - Fiery Cross Base would have to be neutralised - even if it hosted personnel from China plus other SCS countries such as Indonesia, Malaysia, Singapore, Thailand, Vietnam, Brunei etc
One possible model would be the patrols on the Mekong river which runs through China, Thailand, Myanmar and Laos.
The patrols consist of a multi-national, paramilitary force comprised of personnel from China, Thailand, Myanmar and Laos - which means they are authorised to cross territorial borders whenever necessary.