Additionally, you could use the Equalizer (maybe it's an EQ plugin in Premiere) to cut out all the high and mid frequencies of the second edited voice, so you're left with mostly the bass. I think playing with EQ and just mixing the two voices would get you there.

okay, no worries! I'd export the voiceover only, load it into Audacity and use the Pitch Shift effect to get a lower version, then put it back in the editing timeline in sync with the original. Then play with the volume of the lower one to "mix" the two.

Another one that might work is Stargazer by Linda Audio. It's a shimmer plugin, but if you set it to "Octave Down" instead of Up, and turn off all the delays and reverb, it adds a low growl to any vocals.
plugins4free.com/plugin/3966/
I'd use both. Pitchproof, then feed that into Stargazer.

You might want to play around with Pitchproof. By controlling the Dry/Wet amount, you can have the original audio and the pitch-shifted one playing together at the same time, or just by itself.
aegeanmusic.com/pitchproof-s...