Thanks for all the advice folks. So MIG it is then.

What about amps? I need the welder for my machine frame which is mostly 100 x 100 x 5mm, a little research suggests I need something up in the 250amp + range. This should cover 5mm and give me the option of welding thicker box section if needed in the future.

I'm not going to be production welding so how important is the duty cycle? If I aim for something around the -35% @ 250amps, would that be sufficient?