We have been fulltime for 1 1/2 years in a 2011 Carriage Cameo.  Love the trailer.  We have spent the last 2 winters in AZ/CA.  We have had some cold snowy weather in the spring after getting back to Canada & in the fall before heading south.  The trailer handled the weather well.  As long as we kept the furnace on - no problems with water lines.
Whatever you get, we HIGHLY recommend dual pane windows. 
 Being from Canada, you might also want to check out Triple E Topaz.  Triple E isn't currently building 5th wheels (only motorhomes) but they are a very well built trailer if you can find one that suits you.
Arctic Fox is also a good option.  We have 2 friends that have AF & they are very happy with them.