We use the www.Zodi.com instant hot shower. Pretty simple design and very well built. Mine is about 10 years old and still performs like it is brand new. Very compact size, portable and instant.
Put my Anova device in the Sprinter with some water, hooked up to my modified sine wave inverter. Seems to work fine. Perhaps, since the unit is always pumping water at a minimum, it functions fine with modified sine wave. My induction cooktop, however, only turns on and will not produce heat with modified sine wave.