3.2 cubes @ 32 hz, with a single 6" Aeroport should be fine. I don't think you would gain much by changing the ported enclosure size, with the stated input power. You could possibly gain from building a 4th order...
Design yourself an enclosure, and plot out the frequency response graph yourself... Speaker manufactures give out the Thiele Small parameters for a reason... They do this so that you can get an idea for how your subwoofer is going to respond in the enclosure you are building for it. Here is a handy web page, explaining what Thiele Small parameters are.
Now, for a a list of free enclosure designing programs. Here is a list of several different enclosure design programs. Find one that works for you, and research it's features, so that you can figure out which one best fits YOUR needs. WinISD is an easy one that alot of people use.
SpeakerBuilding.com - Software
Lastly, here is the TSP specs for your Sundown Ev2 8 subwoofer.