I use a crock pot all the time, but usually only when I'm planning on being around. Sometimes I add water but usually I just throw in the wax and turn it on. Takes a couple of hours. I've never used it to melt cappings.... yet....
I'm not sure, but I think they're thermostatically controlled at around 200 degrees or so. I'm probably wrong, it likely gets hotter, I wouldn't use it to try and boil water, it would take forever.
We routinely use crock pots for soups and such, they can simmer for hours without ever boiling vigorously.