Since it was running before he cleaned it up, and had already driven it into the trailer, I don't think 150 degrees is out of line. I very much doubt it was much under 100, possible more when he started it for the last time.
How high is the rear lifted? Is it possible that there is less fuel in there than you think, and the pickup is more to the back of the tank, and not in the fuel? I agree that Stabil and Seafoam is not needed (one or the other should be fine), but unless you put in a lot, it should not give you a problem.