Has someone tried to use Silicone Thermal Glue instead of fire cement for insulating the extrude barrel and keeping the nichrome wire in place?

Does/will it work?

I can't comment on that specific glue, and its likely you won't be able to get enough information on it to know for sure, but I'd be quite suprised if it will withstand the high temperatures for prolonged use. In its advertised use for cpus/leds, it probably wouldn't get hotter than 100 degrees, whereas the surface of the nichrome can be much higher than the overall barrel temperature. Fire cement is a huge pain to use, but at least you know it'll last and last. If you're looking for an easier alternative, a fair few people (myself included) have found power resistors a good source of hotness.