Friend of mine runs in a 21 plate DAF with a microwave fitted in the top centre locker, it’s DAF branded 500w, he’s never mentioned any issues with it, I’m sure he said the manual states it can run for 30 mins with out starting the engine ( sounds a bit long, and what the hell takes 30 mins? )
I know it’s on its own in the locker as not much room so I guess a bit more room for the heat, which will be a bit less at 500w?
He just uses a conversion site on the internet to convert the cooking times to 500w and bingo.