Either would be just fine. As I mentioned in my last reply, just be sure that the port is the right length and diameter. When using a thicker panel, there is more length of "duct" simply due to the depth of the port hole cut into it. So please be sure to consider this when making your port, and make sure it's total length is 89cm.On the matter of bracing, the box is small enough that it is pretty solid without braces. Certainly, you can't be too solid so it wouldn't hurt to use the thicker panels or to add bracing. So you won't hurt yourself to go bigger or to add braces.