I'm in the minority, but needing a HPF to protect a ported alignment Is not *absolutely* necessary. It depends on your SPL preference, the frequency content of the source material, the driver's impedance curve below tuning, and any natural frequency rolloff in your equipment. I've been running a pair of Dayton RSS315HF-4 in ported cabinets without a HPF for years without issue. I do have the available power and frequency response to overdrive them according to the models, but it hasn't been an issue in the real world. Typical playback level is -10dB below Reference. YMMV. .
That said, 11 ft^3 seems like an extremely large cabinet, which probably contributes significantly to the excursion below tuning due to the lack of air spring. If you're prone to turning it up to "11", then some sort of electronic nanny is probably a good thing. I don't have modelling software on this computer to see what your impedance profile looks like to see what kind of mitigation that might offer.