I think you may have confused the DC amp draw with the AC amp draw. Truma rates them for 5-6 amps at 12v
, 0.6-0.74 amps at 120v AC.
So, you could just wire up a 12v
connection for it somewhere (if you don't have one handy) or you could run it off the inverter as planned. It's less efficient off the inverter (because you have the inverter's inherent inefficiency, and probably some conversion inefficiency within the Truma) but at 1/10th the draw you were thinking, it probably won't be a deal-breaker.