The Scientific Minimalist Guide to Dead Frontier Boss Hunting now has a chapter on using Explosives to hunt bosses.
Grenade Launchers are not usually a good idea for bossing hunting because they are designed to spread their damage across a crowd of fifteen, not focus damage on a single target.
However, in the eastern regions of Fairview, there are mini-bosses that spawn in groups of five. Using explosives against groups of mini-bosses is very effective.
The strategy can also be employed against Flaming Zombies when they appear in groups, as they do in the missions Flaming Stenches and Big Bang.