I would think the thickness of the metal of the frame would be a bigger influence to failure then method of construction. I know a lot of lite TT use a very lite frame.
The discussions that ensued a few years ago regarding frame failures had finger pointing on both sides of the issue. It was argued that the frame manufacturer(s) built frames to the specifications of the trailer manufacturer. The specs were too weak. Others felt that poor welds, poor construction, etc. at the frame builder caused the failures. Still others including Weekend Warrior indicated that the overloading by owners of more weight than was designed for caused some of the triple axle frame issues at the axle area. Weekend Warrior also incoporated the side walls into the calculations for overall strength and the triple axle length created structural frame issues if the rear toy area was overloaded. At the end of the day those that had frame issues were offered a fix by Weekend Warrior to strengthen the A frames. There were enough to warrant a frame fix kit. It is important to recall that Weekend Warrior was not just the inception for toy haulers but also the dominate force in that RV type for many years. Many many WW toy haulers were made. Even a small percentage of failures were a lot of trailers. Airstream and Keystone also had frame failures. Airstream 'A' frame issues are often cited as being due to excessive aggressive weight distribution hitches. Airforums discusses this. It was not just WW. I have no dog in the stacked frame issue, my comments were directed to past frame failures not being all that rare. Mine has a straight thru frame since you asked and so far no issues.
