4-seasons trailer means it's isulated to withstand ambient temps well below freezing. My personal definition would be down to 10°F., but others would argue it should be down to zero.
Northwood states the Artic Fox is a true 4-seasons coach, with heated and insulated holding tanks, R-18 roof, rigid foam insulated walls, and R-7 floors. I'll bet with the furnace set to hold the interior at 68° F., the rig could handle 10° temps without freezing and bursting anything, but I doubt it could handle zero, especially in a west Texas blue norther. And you don't dare run out of propane, or your rig will turn into a block of ice.
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 EcoBoost SuperCrew.