While that limited-availability connector looks good (thanks for the pics and explanation!), I would also opt for the crimp N-type connectors for the LMR400 cable. You can find antennas with N-type connectors for direct fit, or use a N-type to PL259 adapter.
There is only one way to seal this all but there's an old and new version of it. The new version is much cleaner so here it is:
First, wrap it with Rescue-tape, from bottom to top, overlapping halfway. Rescue-tape is a modern self-amalgamating silicone tape that does not leave a messy gooey substance when you remove it. You need to stretch it to double it's length while wrapping. Once it touches the previous wrap it's fixed forever so be careful.
This tape is not UV resistant however, so wrap the whole thing again with 3M Super 33+ electrical
tape. After some time that can start unwrapping, so I lock it's end in place with a small black plastic tie-wrap.
The old way used 3M 130C tape, plus a first layer of 33+ tape (sticky side out except for first and last wraps). That first layer is to keep the 130C off the cable as it's so messy.