This article will answer your questions about whether a rear door/hatch can be used with a 270 awning attached. When installing a 270 awning on a vehicle with a rear lift gate, mounting height will need to be accounted for. The awning will need to be mounted high enough to clear the lift gate when opened, if you plan on having access to the rear of your vehicle. In most cases, a custom mounting bracket will need to be used to raise the awning high enough (14-20") above the rack height) to give your lift gate clearance.
Check out this walk through video to see how the 270 Awning opens and closes with a rear hatch door.
Another great resource is this pro tips video: