I too, have an ML, and I bought it for vacation traveling and light weekend hauling. I think your idea of running the engine for a few minutes is fine for very old vehicles, but I don't believe newer ones like to sit and idle for very long periods of time.
Try driving it a bit too, if not just for weekends. Keeps the brake discs clear of the surface oxidation that can develop over time, and makes sure that the calipers don't seize up over time.
Tires can develop flat spots if sitting for a long time.
Also, run your A/C, to make sure the seals haven't deteriorated.
I think MBs like to be driven, and I have seen cars that sit for long periods actually fare worse than daily drivers when it comes to wear and tear.
My VW sat in storage for 5 years when I had to move once, and even though it was a show car, I had to practically tear it down completely and rebuild and refurbish everything in order for it to become driveable again.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car