How to put a heat shrink on a ESC?

Hi Guys,

Some months ago I bought a Mamba-25 ESC, but the heat shrink around the ESC tore. Ok, so now I want to put a new over the ESC, but how should I do this? Because castle has done this very well. Look at this pic:


How should I do this? And it should be tight around the ESC, not loose of course


Thank you,

Patrick