A while back I was browsing the interweb looking for a mig welding cart. I didn't find anything that motivated me to make the plunge but I did see a weld cart/tool box from Northern Tools that got the creating juices flowing.
I started with an old Craftsman rolling tool cart, I built a frame around it with 2" x 1/8" angle iron, added a platform to hold the tank, then mounted a piece of scrap plate steel on hinges to create a fold down portable weld table.
It's not pretty but it's practical.