The reason that the OEM'S
DO NOT SOLDER their connections - EVER - is that heating the copper embrittles it... and then you have the softer copper right at the end of the soldered connection which becomes the break point. Solder is used to attach wires etc to circuit boards. It's never used in a Marine or Automotive environment.
Trust me that you'll have a far better crimp using the uninsulated butt connectors (uninsulated terminals period) using FAR LESS pressure - over the insulated versions... and all the shrink tube I use is GLUED type. So moisture is never an issue as well as it provides the strain relief at the connection.
No wires should EVER be hanging - or be allowed to vibrate or chafe.
Here's an example of proper wiring....
And one of how not to do it......
