Don't do that. It's the worst. Someone did that to me once and it's incredibly hard to convince others that it wasn't YOU that pooped YOUR pants. Such a mean thing to do!
Yeah I guess heat-shrink would do the job most of the time. But for when you have connectors that are too big to fit the right heat-shrink over or want to splice more than 2 wires together and want a waterproof seal over them this could be useful.
I'm positive I saw a purpose-built stick out there for use in this application. like you can run it through any regular glue gun but you get rubber out the other end