Great progress Chris!

If I can make a couple of suggestions?
Put in as much natural lighting as you can, translucent roofing sheets are supposed to be good.
Another is to build in at least one strong point, reinforced trusses etc, so that you can easily lift things off your truck or trailer, even if you have an engine lift you might not be able to lift heavy stuff off the middle of your trailer. My last suggestion, which worked out very well for me, is to put power points in the ceiling.
OK, thats enough from me...