I happened on this video that showed a method of PL-259 installation that I’ve never seen before and it works VERY well. I’ve used this method the last dozen or so times I’ve installed connectors. It’s a bit dragged out but still good info. One of the most important things he mentions is the size of the soldering iron. A LARGE low wattage iron with plenty of preheat time is important. In this case ‘Size Matters’. It’s like wok cooking, high heat for a short time. The large iron has a lot of thermal mass and quickly heats the connector to do the job. Practice makes perfect.