I did consider that in the model, but port air speed won't begin to be a problem in this design until 22hz or so and only at max output. Given a 28hz tune i mentioned in the model,he could fit it in there if the box is 24x24x24 with an elbow at the inlet-i've used em before with no ill effects. I agree with you that 2cubes isn't much to work with. I'd mention a
PR design but the OP may not have the tools to install them in his box. If he does, then i would suggest 2 side mounted 15 PRs from AE-At 500watts that would be some sub. The 4" port i offered in the model will displace about .18 cuft internal volume and given his box size-resultant is around 54L. The design can and will work with some tradeoffs as always. I offer it as the most cost effective relative to box size. If the OP is still listening and is interested in a Passive Radiator design-pls inquire.