Your first clue that you're looking at a rig not intended for winter use is simply to look at the sewer valves: If they're visible under the rig, then it's not for winter use.
Insulation may not be the type that simply wraps around a pipe directly; rather, the pipe or tank may be inside a compartment that is itself insulated and heated.
Note, too, that using a bit of RV antifreeze in tanks is not a great solution. That antifreeze is not intended to be used in a diluted state, unlike automotive antifreeze.
:)
Lynn