I used a 20mm hole saw to cut the required corner radius and then removed the floor sheet with tin snips leaving about 10mm around the edge for a final neat cut. The Z angles where then cut to size and clamped to the floor which was then flipped over and the Z angles back drilled with a #40 drill. There is still some extra reinforcement required by the additional of a few extra Z angels to the sides of the fuse longerons and then the hinge and door get fitted.
Rough cut out of rear access door
How it should look after cleaning up the edges
Z angles fitted to the the door surround, extra side braces still need to be added
