Its likely that you may have a hollow like sound to it, due to the fact that it will be used for midbass. If there are any panel areas larger than the cone diameter total, its likely that the panel will cause undesirable effects......ringing maybe not so much, but a muffled sound, very likely. By adding a material that is more dense than the types of wood we normally use, you are giving it a higher degree of reflection within the enclosure, so ratios of width, height, and depth may have to be carefully followed. This is different for subbass frequencies, as they are too long to make a difference at less than half wave resonances in most cases, but when you increase the frequency range, you may end up matching the natural resonance of the aluminum, which will only excite the panels even easier. So bracing, as you mentioned is a must. I would also line the inside with fiberglass cloth insulation as well, with a high density material rating. This will help with reducing a possible tube-like sound from the port.
Bracing and inner dampening is beneficial. This can be done if done right.
