The only thing with 2x4s is that you're taking up a decent amount of air space. Not a ton by any means, but probably more than necessary. Chris, I would suggest you use one of the options M.S. suggested.
I'm confused, how does rounding over the corners of bracing or for that matter not rounding over bracing effect the overall resonance properties of an enclosure??
I could see if the bracing was directly impacting the port area portion of the enclosure ( which would be totally stupid ) to have bracing in such areas.
However, if there is verifiable proof ( I'm talking actual proof, not someone's statements ) that given a manner in which bracing as to types used as to where applied/attached within the confines of the enclosure's interior creates noise resonance issue's.
And Yes, I have heard all the debates, arguments and such discussion on the issue of bracing and for the most part while different types of bracing ( threaded rod being one ) does impart advantages over over types of bracing, that only really applies to the design of the enclosure for the intended purpose trying to be achieved ( SPL Comp Type Enclosures ).
For everyday listening and head bangin enclosure's, one type of bracing over another is of or has little effect, let alone be able to tell/hear the difference's.