Time and motivation for me, I got all the stuff I need for it and have had it laying around in various parts of the house for months, shouldn't take too much longer though as I've broke the back of it, still need to fully seam weld the inner sill to the box section underneath and get it all seam sealed and painted properly under there but that sort of stuff goes really fast compared to fabbing up repair plates and fettling them into place, I could have saved a load of time if I had just spotted plates and patches in place and seam sealed over the top but I want it to be fit and forget with regular applications of rust preventative solutions.
I must admit that the rear door post has really thrown a spanner in the works as I hadn't expected anything like that to crop up and it'll take some figuring out on how to fix it properly.