4 Season is relative. Will you winter in the Florida Keys, or North Dakota? You'll probably be ok in the Keys. Not so much in North Dakota.
Any ultralight will have lesser insulation values in walls, floor and ceiling, if you'll be in a sub-freezing climate, you'll have the furnace running a lot and you'll be using a lot of propane to keep the living space warm.
Keeping water running is very different and you may have to do a lot of extra things depending on how cold it gets. Take a look at our owner-written Water Systems Winter Usage Guide.
The Sundance line is not designed for full time living, it is more of a recreational trailer. That said, you can make some modifications to make it work in various weather conditions. However, the fridge size, limited storage, and smaller holding tanks may "cramp your style" if you want to use it to live in full time.
What we did when searching both our RV’s were first go look up all the recalls on them, if any. Research all that it is suppose to have pertaining to seasons. Not all RV’s are made for 4 seasons. Check warranty and the place you may get it, check their reviews. This is a start for you. Hope this helps.