Liquid electrical tape as a seal also works, and sticks to PVC well as it is solvent based and chemically bonds to the PVC itself. The glue lined shrinks do work well, and you can use them as a cover for the join, followed by wrapping with regular 3M insulation tape and then overcoat with self amalgamating tape, then cover with more 3M insulation tape and a final coat of liquid tape to make a join that will still be there when the rest of the cable has disappeared from UV exposure, and the copper inside has corroded away.