Thanks guys. I had put it in the center with the plans of adding a 2nd v-vessel on the opposite side (sandwiching the 2x6). I just used 48" 2x4s for the 2 "posts", the bracket for the v-vessel (black) is attached to a 2x6. I made the base 2x4 ~36", and its about 24" wide. I used almost 3 8' 2x4, 16 x 1" lag bolts to hold the casters (2 being "crazy"/rotating with wheel locks), and some lag bolts just long enough to not penetrate the stacked 2x4 portions.
With the cross bracing and such it is very solid.
The v-vessel itself does not have any handles, which is the one area of weakness I have seen so far. I have so far picked it up by the round posts that it hangs by, but that isn't very comfortable and you wouldn't want to carry it very far. It has a batch of the NB "XX Ale" stock/old ale in it now, bubbling away.