OK...here's the truth. We fulltimed in a Bighorn for almost six years. Put over 80K miles on it. Spent time in temps from around zero to over 100 degrees with no issues. We did have dual pane windows and two a/c's...this was a 2008 model.
Loved it so much we now have a 2013 Landmark (different floorplan)...have been in it fulltime for over a year. It also has dual pane windows, added yetti package (which will get a work out tonight...temps in TN are suppose to drop to just below zero)
Have never had a frame issue on either...running gear was a bit of a problem, so we had Mor Ryde IS added to the Landmark. However, they now offer 17.5 tires and rims and disc brakes along with 8K axles...which became available several months after we ordered. Also you can now get a residential fridge, which I would have ordered if it had been available.
Others will try to tell you these are not fulltime units...our ACTUAL experience proves the opposite...the Landmark also has a 2+5 warranty and is warranted for fulltime use, as is the Bighorn.