I have just happened to drop onto this thread regarding rust on MG ZS EVs, I wish I had seen this before purchasing mine new 21/1/20. Mine has now covered around 3600 miles and is suffering from quite a lot of corrosion.
It has rusting evident on both Front wings where they bolt to the inner wings along with other under bonnet corrosion.
NS rear door has corrosion
There is also several areas on the floor pan where rust is taking place.
Presently the windows and both door mirrors have stopped working, unfortunately the dealer cannot get to it until 9th October 2020.
My advice would be to consider other options before buying an MG.