Any microwave will do depending on your power reserves and inverter, or will you just be running it off shore power?
Microwaves are one of the simple appliances to apply to DC voltage RV life because we are all familiar with them in watts. You need to remember that there needs to be some flex in your setup though. If you have a 1000 watt inverter it doesn't mean you can run a 1000 watt microwave. I have put a 700 or 800 watt microwave in many van builds, including my former Transit, with a 1500 watt inverter and 200ah of batteries. With this I still only got seamless performance by idling the van when cooking.
No microwave is really designed for the vibrations and rigors of being in a vehicle but after killing a few I have learned that honestly the cheaper the better because you'll likely be replacing it at some point.
This is my favorite of all time, recommended by someone here (link below). I sold it with my Transit and it was still humming along nicely.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1