I've been working on stuff long enough to know that I don't want to be dragging a huge rolling tool shop around when all I REALLY need is the welder, and vice versa, so I made my own welding cart, just a welding cart-----if I need a wrench, I'll open my toolbox and grab one, no big deal, it doesn't need to be on the same cart as my welder!
BTW--paint was still drying in this pic, but it should be pretty clear what's what---welder sits on top, bottle below, MIG gun in metal pipe 'holster'. This was built from a dissected and re-built hand truck. Even the corner gussets, which were originally the hand-truck bottom plate!