I repurposed the steel and a window from the original door and a proper car door latch to make a completely different, one-piece door. It was a quick and dirty job, though, and it is fundamentally flawed in that it is nearly impossible to seal. Tough as nails, though. I'll be making a new one out of angle iron soon.
I know a lot of people use residential doors, but that doesn't sit well with me. I used residential door latches for other uses inside the bus and one has already failed from road vibrations. Would hate that to happen to the front door!