Acoustically the bottom of the enclosure is fine, but a heavy cone will indeed sag eventually.
A bigger problem is that your port
a) looks too close to the cabinet panel to be able to flow properly
b) is backing up directly onto the cone, which will be pumping air right at the port and also interfering with airflow.
c) 4" is generally too small for a 12"-check the airspeed if your box simulator will do it, otherwise I'd go at least 5." Yes, ofttimes the "ideal" ported designs just aren't physically buildable.
So yeah, redesign time.
And DON'T put elbows or kinks in the port! C'mon guys, it's common sense that will not flow air well unless tremendously oversized (and probably not even then).