So I've looked into it, but in it's current State the A300 is sadly not ready for an external GSX Integration/Automation!

• Cargo Main Door not toggleable in a Way for GSX to open the Door by itself AND not any Command available for that Door so that another Program/Tool could open it for GSX
• Fuel can't be set from Weight & Balance - using the standard SimVars to implement an external progressive Refuel is not possible with that. So there needs to be somekind of Variable that can be written to with the Fuel Amount to set (which could be used to lower/reset the Fuel - see below - and could then be progressively increased). 
• Also: the Default Fuel Quantity is way to high. To get a proper manual Fuel-Synch with GSX you have to load the Plane twice (first to a low Value, then to the planned Value when the Fuel Truck is connected).
• The Payload Stations seem to work and therefore useable for Pax/Cargo Synchronization, but a simple Variable to set the current Pax Number and/or Payload would be easier.

I could manage to get the Ground-Equipment automated (Chocks, GPU). But although the respective L-Vars trigger the Chocks and GPU correctly, the State is not reflected correctly in the EFB afterwards.

Heya!

The first one is a GSX limitation, as it can't open doors with a custom LVAR.

We will look into the other three 🙂