You can also get self vulcanizing tape specifically made for high
voltage splices. Get it at an electrical store, no HD or Lowes.
then wrap that with lots of electrical tape.

This stuff


" Scotch® 23 Rubber Splicing Tape is a highly conformable, self-fusing
Ethylene Propylene Rubber (EPR) based high-insulating voltage tape.
Scotch® 23 has a "snakeskin" liner that is easily removed as the tape
is applied. "