Devon Dweller

The resting voltage approach works, but you're all skirting round the real issue — internal resistance.

@FormerMariner the engine bay is a non-starter unless you're planning on replacing it every couple of years.

The real issue isn't the inverter voltage—it's the cable run and battery bank capacity. @WattKaren, you've already got the Victron sorted, which is the sensible choice for workshop use.