The vapor lock issue is an interesting one, on it's own. I am not versed in it. I did however, have an issue similar to yours some time ago. I thought it was vapor lock. I would shut it off to get gas, and it would not restart. It would crank, no fire. Let cool, and it started. This happened 3 times, the last time no start at all. It was relay #5 and I'm fairly sure what I experienced was that it failed "gradually" .. similar to an incandescent light filament that will break and sometimes repair itself.
It gets hot in Indiana, and I have a fuel filter between the jugs. I've never had any symptoms of what I might describe as vapor lock, other than what turned out to be a failed relay for the fuel pump. What were your vapor lock symptoms?