True. Plus when I was recording last weekend, I wasn't sure if I was getting too close to the mic or had the gain too high and thus sounded "boomy", or if that was a good thing?
The closer to the mic you get the less the 'room' sound will affect your recording but, depending on the mic, getting very close (less than a few inches) and you will have proximity affect boosting the low end. This is very obvious within a couple of inches but can be tamed using eq as long as you keep the distance constant.
So as asked above, can I just build a tiny sound-treated cube around my head and mic, or do I need the larger open space treated?
The V/O artists in that article build a small 'booth' and work close to the mic. There shouldn't be any need to treat the rest of the room if the 'booth' is sufficiently effective but you will probably need to use a fairly aggressive HPF to avoid 'boxiness'.