What to look for - construction / materials / options

Sorry, I just read the post again.
Construction will vary as well, full profile, mid profile etc. The frames, while they are I bean and Tubular, I believe they are obvioulsy made to hold the home that is nbuilt on it. Just try to make sure you get a good insulated one,and again, tap the rv forums to get actual user info as well as the structural process from the manufacture. If you can and are near a manufacture, take a tour of the factory.