Why?
Your bracing will stop vibration and your PolyFil will provide any needed damping.
Don't take this wrong but if your taking any advice from people who have made guitar cabs:
Ignore all of it.
Its worthless pseudo-science based on what some rockstar in the dark ages did.
Electric guitar and it's amplification is the most forgiving part of acoustic theory. Anything you've seen in a guitar cab: forget. They can do everything wrong and produce a sound, and with enough gain it sounds fine anyways.
If this cab is for bass guitar and you hope or will perform as good or better than what you have, stick with the science.
Your trying to make a box that produces sound where the human ear is very insensitive, where amplifiers work the hardest and where speakers need certain things to work well. Every compromise made for "pretty" is a risk at performance loss.
Do you want a cabinet better than what you've got?
Or do you just want something you've made?
When you're modeling you're old cabinet, what you probably aren't taking into account is things like: losses due to panel vibration, small leaks here and there and thermal losses that hit you at volume.
All of those things being the cabinet farther away from your ideal model, bit by bit.
Building a solid box, without leaks, damped properly will get you much closer to what you've modeled. Then that 3-4db 5hz lower is actually a lot more like 5-6db across 10hz or more, because you don't have minor losses here and there.
Oh yeah, precision ports are a good choice.