Pete, that definitely won’t work at watertight, no matter what the advertisement says. There is not enough “adhesive” in those connectors to bridge the gap between 2 round wires side by side. You can tell this by the illustration, the lack of apparent thickness of the “adhesive” and the fact you can almost see through it. Both say “thin coat of adhesive”.
Look at this site… scroll down to “heavy duty adhesive lined”… https://crimpsupply.com/shrink-tubing/adhesive-lined
That black “heavy duty” stuff would work, it has a lot of “goo” inside it… look right below, and you will see your yellow butt connectors, and that they do not say you can use multiple wires, while the black stuff says explicitly.
That’s why you either have a connector with multiple round ports, or you use the ScotchCast “bag of epoxy” or get the really heavy duty stuff… …
That connector will probably be waterproof if you put a single round wire in each end, but in my mind, the amount of “adhesive” is questionable except for very smooth and round insulation and one wire each end.
(by the way, living in San Diego, I have been to West Marine many times, since 1972)
I’ve done electronics on boats, buried lots of landscape wire connections (I have about 12 separate landscape circuits, all buried in ground that actually gets wet and has lasted 20 years), and done a lot of wiring on the tops of amateur radio antenna towers.
The bottom line, water will work it’s way into any gap eventually.
Greg