I don't consider Prime Time a "premium" unit. Same price range as my Rockwood.
Looking at the features and so forth when comparing the Prime Time Lacrosse to the Rockwood I had, the Rockwood was just as good or actually it had a few more features. The difference is in the construction. Different materials and methods. Prime Time places a 25 year warranty on the roof, floor and all water connections. The slideout walls and roof are constructed the same as the rest of the tt, so it's OK to walk on the slideout roof. After final factory inspection every unit is taken to a seperate facility and checked and tested once more before shipping.
On their web site there is a link, Eternabond Construction, explaining their construction. Here's the link;
Prime Time Manufacturing, Manufacturers of travel trailers and fifth wheels
I'm not trying to put down the Rockwood or Flaggstaffs, nothing wrong with either unit. Just noting a few of the differences I found.