Try this page for options:
http://nordicgroup.us/hotelcooking/
I travel with an immersion heater and an insulated steel bottle/Thermos to cook the water in. 240 V immersion heater if I'm going to parts that take it and 120 for the others instead of a dual voltage heater. Also keep in mind that there's no auto-off sensor immersion heaters and you should unplug it once water is at the desired temperature. They fit in the Kleen Kanteen insulated 12 oz bottles. I do have the Narita air pot and one of the inexpensive electric hot pots but the immersion heater does the job in a lot less space.