Contents Box / side paneling left back at the tailgate?

Hello Ford community, I’m currently looking for a transit custom for a buddy to have it upgraded as a camper. That’s why I’m looking for one without interior trim – because the vehicle is being insulated and re-dressed during the conversion. Many cars in question have a very wide panel at the left side back (see picture). So far, I assumed that the heater (at least component such as ejectors etc.) is installed among them. But this space-consuming panelling ng also have vehicles without heating. So what’s underneath and can this panel be removed without any problems? Thank you very much, Greeting Daniel