If this speaker is destined for PRO audio use, it will bashed around a good bit. External finned assemblies will be destroyed quickly. Perhaps recessing the radiator fins would help, or a mounted heat exchanger in the walls of each chamber would work. Also, keep in mind that if the OUTSIDE (the chamber temp is higher than inside, the heat will be conducted back into the speaker.
My take is to build one without any extra plumbing, try it, and decide if power compression or outright destruction is an issue.
( I bet not...)
Also remeber duty cycle will allow for cooling, etc.
Larry