All depends on how much and what kind of bass you want to make.
Generally, the rear doors are a poor choice for sub-woofer location.
Doors will rattle and bass will be less accurate and defined.
It can be done and door/panel can be reinforced if you desire.
But if only moderate supplemental bass is all that is desired, then this is a fair compromise.
You'll get something.. but far from optimized.
It's not a bad location if your preference is not to lose space.
Rear firing a sub-box toward rear doors, or upward at rear doors will usually give deepest lowest loudest bass throughout entire vehicle. It will act somewhat like a bass-loaded horn and have the space to make a waveform. While this may often be the preferred method (for modern music), it's not really for me and rock and roll sound.
If you prefer less boom and more bump or full rounded bass, then something near driver will work. Behind the driver seat, or between seats (firing downward) are good compromises too.
There is no right or wrong.. just what works for you