This is exactly what the 2018 manual states.....
Your vehicle is designed to operate on
regular unleaded gasoline with a minimum
pump (R+M)/2 octane rating of 87 or
regular unleaded gasoline blended with a
maximum of 85% ethanol (E85).......
For best overall vehicle and engine
performance, premium fuel with an octane
rating of 91 or higher is recommended. The
performance gained by using premium fuel
is most noticeable in hot weather as well
as other conditions, for example when
towing a trailer.
It never states that premium is required when towing. It just stayes that it is recommended IF you want the best performance and it will be most noticable in heavy tow and/or in hot weather.
