700w will be approx 1100w power demand from inverter. Check the back of the microwave.
So approx 5 amp at 230v will be roughly 53 amp from batteries if 24v inverter and if inverter is 100% efficient which it won’t be.
Ideal solution would be Anderson lead protected by a mega fuse. Is mp4 the new shape Merc? There should be spare mega fuses in the box attached to the 24v power point on near side under cab at back.
Mine has the Anderson plug on near side all I did was run cables through locker into cab and mounted inverter behind passenger seat and put a new 100 watt fuse in the box at side of plug