I would suggest to compare a few different brands, just so you have an idea how they are built.
I would look at the frame, how deep it is, and how thick the I-beam flanges are. Note that some campers do not even use a real I-beam, but make one up out of three pieces of sheet metal, and those are much weaker.
Check to see if they have aluminum framing in all walls, roof, and floor. Some have no roof rafters at all.
Make sure the floor has at least 5/8 ths inch plywood on the floor. Some have nothing more than a thin veneer of "plywood" underfoot, and are prone to failure.
Compare the thickness of the walls, and insulation values of the walls, roof, and floor. There is a huge difference between campers.
And lastly, just look at different brands, and even different lines of the same brand. Check out their fit and finish, as it does vary widely.
And when you finally decide on a particular camper, see if they will swap out the garbage factory tires for something like a Maxxis or Kumho.