Now I have the unit hook-up and working, the unit blows out very cold air, most of the time it is in the low 50's, and some times even lower.  It's so cold that I cannot keep my hand over the vent.  Next I had to build a cover for it, but I drove around with no cover for almost a month, then finally because I was going to have kids climbing all over it while it was at a fund raising thingy for Special Olympics I had to come up with a cover.  Got some 3/8 thick cabinet wood, and made a simple durable cover. The cover came out great, now all I have to do is get it covered with some soft vinyl like that of the dash. Just below the cover, I put some black rubber foam to prevent it from squeaking, and foam also below the vent to make it fit tight and to fill in the gaps. The cover also worked out as a nice arm rest.

I also added an extra vent from the front AC Unit since the vents are no longer going to the rear.  It is located so the front passenger could have more air. The vent & hose came from the old rear vent supply.

First I marked the area that I want it at, drilled the corners, and cut an cleaned the opening out with my Dermal tool.

Still the A/C in the Hummer could be better, so I am looking into more changes.

I have since covered the box, and will have to add a few photos.  Here is also another Hummer with a custom AC unit that was installed in the rear area and covered by the kiddy's bench seats.  This was is great, give the kids more leg room and makes the inside more opened  in the center area.  The AC unit was also for a Corvette and fits well in the rear and lots of air.  Also made a great area for the speaker that where mounted in the base boards that was install but was too dark to get any good photos. - Click on the photo for a larger picture.