Side-chain-gated signal generator works very well in Cubase, with good control over the decay (and attack, if wanted).
Rather than stick with 60Hz, I try to tune the note to the root of the song (e.g. A = 55Hz) which seems to make it fit in nicely!
+1. Cubase's Monologue synth is fine as a source for the sub signal. An alternative way of achieving the gating in Cubase is to use the Variaudio audio-to-MIDI function, and then use that MIDI signal to trigger as instance of the MIDI Gate.