A week or so back I bought another MIG welder. It is a medium size one and so is portable. I have a bigger industrial one that I bought new in 1976 which is far from portable. One of the first jobs that I used the new one for was to make a trolley for itself. I just wanted a simple support with the only "special features" being some cable supports. The electrical socket on the bottom rail is not connected to anything, it is there simply to stop the plug wandering when not in use. I think that a lot of things should come with such a dummy plug.
The only things that I had to buy were the casters, 16 euros for 4. Everything else came out of the scrap box.