I had some water leaks in my TT. It had thin alum covering the whole bottom. It had pink insuluation resting/setting on top of the alum just under the floor. What I didn't realize is if you don't put the insulation back in, the thin alum will flutter going down the road and will eventually crack/rip from fatigue. In other words, the insulation was in there for 2 reasons. Insulating and the weight would keep the underbelly from fluttering. The area where I didn't put any insulation in was only about 3 foot square. Even that small area did crack and rip going down the road.