Blimey! Two nights in one week! What's going on? I spent another 1.5 hours working on the car last night and managed to remove just 12" of metal! The reason it was taking so long is because I was trying to remove the metal that were it had been welded to other panels so I had to go at it carefully. A combination of angle grinder, drill and big chisel sorted it out! I managed to drill out a few of the spot welds but some of them just wouldn't drill out so I ended up grinding all the metal away until the weld just let go!
Although I didn't get much metal taken out I feel like I managed to make some good progress.