I got my remote security rig assembled and configured. Kill-a-watt confirms 25-30 watts. I ran it for a day to check kWh measurement against real time and it checked out.
So yesterday I fully charged the EcoFlow, plugged the "rig" into that, and pulled the AC plug. The readout suggested a 22 hour runtime. That's less than the 33 I calculated, but there's overhead and waste associated with DC to AC to DC, plus heat and cooling fans.
Anyway it ran for 20.5 hours before I plugged it back in. Still had 13% battery and ~3 hours runtime. Very positive test, I'm pleased w/ the results.