Terrib972, our 2109S has the open under-carriage. I did have the tank heaters installed when we purchased. We have camped several times in mid 20 degree weather at night without any problems. I turn on the tank heaters, disconnect the hose and run a little water once in awhile during the night. For even colder weather you can leave the anti freeze in your lines and use bottled water for brushing teeth, toilet etc. and use the tank heaters on your grey and black water tanks. So far no problems. I like to stretch our Minnesota season as much as possible.
Welcome to the forum !
Ps. I had the park to myself!