haha! I had no idea. I know you can use ARX to modify ships and SRVs but I haven't collected enough to use them for anything yet, so I've not taken a detailed look.Well first of all (and I can't quite tell how serious you're being) that's actually an SRV parked behind a Mamba.
As for the big orange spoiler on the back of the Mamba itself, that's a paid for ship kit and is purely cosmetic.
Having said that ... you can stand on it so I suppose it does serve some very small purpose as a viewing platform.