It doesn't matter how the walls are made. If there is a leak-seam, window, joint, clip light,etc. and water gets in, there will be damage. I learned on a new trailer, assuming all was well. It wasn't.
My recommendation--regardless of the trailer, mfg., or type of construction, I would make it mandatory to have a pressure test done and ALL leaks repaired (yes, there will be leaks) and re tested. If the dealer is hesitant, I would be inclined to ask why, if the trailer is that good.
Next, this does not end the process, yearly you have to inspect and recaulk and I would still periodically pressure test. Only way to tell if there is a leak is to see it.