If temps will reach the mid-upper 20's for any length of time, you need to take measures to prevent the plumbing from freezing up. If you set the furnace to say 45+-, you should be OK. Relying on an electric heater inside is a ****-shoot, as it may not provide enough heat to all areas where there is plumbing. e.g.does your TH have a rear bathroom?
Last concern is that if the RV is unattended, what happens if power goes out and the temps drop? Murphy's Law is always lurking..........
I can winterize my Cyclone in 45min. That includes the rear bathroom, washer, water heater, main bath and kitchen areas. I'd say if there's a chance of damage, it's worth the minimal effort to winterize.
Paul & Sandra
Plymouth, MA
2014 Heartland Cyclone 4100 King