Most likely it will be a troop transport compartment, making the HAVOC an IFV. This could easily be converted into a space for non-human cargo, and with a bit more effort it could be something like an AA turret back there. There are a few cool options, but the trick is to make it unique from other vehicles. No version of the HAVOC will be amphibious, which will give the GI Joe APC some job security, but the variations I mentioned begin to illustrate how creating too many versions of one vehicle can make the other specialized vehicles less special and thus less necessary. I want to give due diligence to as many vehicles as possible.