Have you thought about buying used?
SilverBuffalo is correct w/ his analogy of the packed garage.
I purchased a used ZZ trailer, and on our first trip I had that thing plumb full with all sorts of stuff I picked up along the way. While I've been trying for years to travel lighter, whether on a bike or taking a plane ride, the end result just would not fare well with something so small as the uni-go, especially considering the price of these new. I have suitcases larger than these.
So, maybe this could be the deciding factor for you- What kind of traveller are you typically? Do you tend to take everything, including the kitchen sink, or is it more like needing a wee-bit more room in order to buy that unusual/rare find during your journeys?
Back to my suggestion of buying used. Obviously, logistics issues come into play as far as how to take delivery of it, as well as whether the additional related costs would still make it practical. In my case, it was still a good deal, even after the seller did a very professional job of crating it and Fed Exing it to my designated receiving point. Naturally, a little patience will be needed for the wait for a suitable one to come available, but it sounds like you already have that being you've been researching a few months now. I actually had a few choices pop up rather quickly, but the ZZ's styling and it's very helpful and friendly seller proved to be the one for me.
If you don't already know about it, check out www.searchtempest.com
It's a search engine that allows one to look for anything sold thru CraigsList within a chosen radius, including nationwide searches. It also includes Amazon and Ebay results if desired.
Don't have an answer for your storage limitations of the trailer itself. Maybe it'd fit in the attic when not used?