It depends whether you wish the join is to be permanent. Of course the connector must also suit the use (depends on voldage, AC/DC, or antenna coax etc) If permanent, put a heat shrink sleeve on the wire - solder and insulate the wires and then heat shrink the sleeve into place over a blob of silicon sealant. Alternative to sleeve and sealant is self-amalgamating tape. If not pemanent, look at chandlers for bespoke solution or RS Components (rswww.com) who have endless selection of high grade connectors.
Alternative to using lined (adhesive inside) heatshrink and much better than silicon mentioned in an earlier post is to use unlined heatshrink after roughly coating the joint area to be covered by it with hot melt glue. The joint is not so flexible though, but usually that does not matter.
The heat from shrinking the heatshrink will remelt the glue and the compression will spread it - I always have hot melt and unlined heatshrink but not always lined heatshrink of the correct size.
If silicon is used near conductors it must not be acid curing.
If a joint made with a line connector then use self amalgamating tape.