The fuel tank is too big. When running in the past I've just kept a close eye on it. When it stopped I would turn off the gas. At this point the boiler would be out of water. As far as I can tell, there's been no damage to the boiler from this.
As I was saying, the fuel tank is too big. Rather than make a new one, I'm just going to displace some of the volume. I drilled a hole in each side and soldered a 1/4 inch bar in place. The holes were countersunk to give space for solder after sanding the joint flush. Also more painting.