The method, as taught by the Union - so it's likely buried in the NECA standards somewhere - is:
1) 'round out' projections with electrical insulating putty;
2) Wrap several times with self-fusing rubber tape; and,
3) Finish with a two layer wrap of ordinary electrical tape.
The inner tape, and putty, fuse together into a solid rubber block, so you're not going to ever be able to unwrap this assembly; it's time for a sharp knife - and patience.
Some will start off with a layer of 'glue side up' electrical tape, with the idea that this will make taking the thing apart easier .... but I worry that this practice will result in the final assembly not being as waterproof as it should be.
