The cardboard is a temp fix for now, I will most likely replace it with something a little more waterproof. I was looking at something like a pool noodle cut in half. The cardboard used however is more of a composite material, not to mention it is almost 1/2 inch thick. If I decide to stick with this material I may see about coating it with some kind of sealer to prevent any water damage. I also live in a desert so I do not plan on getting this guy too wet ever. Also this top piece offers no real structural integrity. If my actual mounting points fail this does nothing to hold the tank down. It only adds some girth under the tank.
The issue with the new tank is that it has a much deeper and wider well underneath and I needed to have some of the space filled tighter or I was afraid the bracket in the front and the where it will be held in back would be weakened as the tank would shift while riding and eventually cause it to stress and break. This helps sturdy it up a lot more. I also don't want to alter this frame from stock. Especially not welding more weight to it. This way or a fun noodle way adds little weight and also provides some padding to let the tank not sit just on a stiff hard surface. You know a little bit of some vibration dampening.
I appreciate the concern and kind words regarding my build. Since I am limited to my own workshop for fabrication, I need to be less limited by imagination. I am also not trying to convince anyone that this was a genius solution and to try it themselves, but just a glimpse into some of my ninja-neering. When I come on a better solution I will be replacing this for sure. Only 3 clamps secure it to the frame so removing it is easy.
Thanks again everyone for looking over my build thread. Please keep the comments and ideas coming.