That is not a tank. Its a wheel well, and its wrapped in sound insulation. They are large, flat, and very thin walled...In other words, they are like a drum and will vibrate and make noise. This stuff dampens those vibrations and will hopefully quiet the travel experience quite a bit.Why did you wrap the whole tank in insulation?
On the photo site Rob Mueller posted adding a marine deck plate to the top of the tank for cleaning access. I've adopted that when removing or replacing a fresh tank.