I have a sunseeker with the arctic package and have used it while driving down to about 10 degrees with no issues. Never really used the tank heaters when parked since if it's cold enough to worry about freezing, I'll have the furnace on which heats the basement.
As for the heat pump, I've used mine successfully down to 30. Even through, it's really not supposed to work well in temps that low, mine will. Now, the propane furnace heats much faster and feels warmer below about 40. One thing to remember is the heat pump does not send any heat to the tanks and wet bay. Only the propane furnace does that.