Grey and black tank models for underneath

The next job to complete is ordering all of the water (fresh, grey, and black) tanks for Redford. The black tank will be installed on the driver's side and the grey will go underneath on the passenger side. I made a small modification to the muffler heat shield on the passenger side by bending the horizontal flap downwards. I'll also install some heat shield directly onto the side of the tank after it has been installed. I was trying to figure out how to make a tank that would optimize the space. I came up with the idea of using individual cardboard boxes (12"x10"x8"). By taking one box, I could slide it along the cavity I wanted to use to see what the clearances were like. Once I determined the best dimension to fill the space, I created a stack of boxes by taping several together. On the passenger side this allowed me to locate one particular cut out and also check about the drain pipe location. The black tank on the driver side will be a bit simpler in that no cutouts are needed. Both will be trapezoidal prisms. The black tank will be 12" wide (a stack of 6 boxes) and the grey can be longer (a stack of 7 boxes) but only 9.5" wide. Each tank will hold about 26 gallons of water. I'm taking the model to a tank manufacturer tomorrow to see how much it will cost to build - but this is a common process for people who make boats as they are always trying to optimize space utilization. Our fresh water tank will be located inside the van in the back of the passenger side behind the wheel well. That tank will be about 40 to 45 gallons in size.