I got the door for the water heater all sorted finally. It took a little more doing than I had anticipated. I cut the rough opening in the front wall larger than the water heater. But once I put the trim for the door seal in place, the opening became too small.
I notched the case around a hinge to move it closer to the hinge side. I'll probably end up having to box that area back in somehow. I'll need to do some testing to see how hot it gets first.
Anyway, other than that, I'm really pleased with how it came out. We fiddled around with the hinges yesterday trying to get the panel gaps just right. They're really close, and as good as we can get them. Nothing gets hung up on opening and closing, and the door ends up pretty darn close to square and centered in the opening.
I also drilled then shaped the holes for the latches. That was more difficult than I anticipated it being. In the end, a piece of sandpaper wrapped around a threaded rod worked really well. I just kept repeating sand and check. Sand and check. Sand and check, until they fit in there snugly. Also, we spent longer than I figured it would take trying to orient them so that they're both righty-tighty and oriented the same in the lock and unlock position. But it was time well spent. The action of the locks feels very solid.