I live in a mobile home and have a 125 gallon tank running parallel to the floor joists. I for one can tell you that this was a recipe for disaster. One of the floor joists under the tank shifted and the whole tank leaned back towards the wall around 2 inches. I was home when it happened and there was water spilling over the back of the tank. miraculously the seams and the glass held. This was 8 months ago and the tank is still up and running. I have since reinforced the floor to the point where a tornado could take the house away but the tank and that part of the floor will still be there. I doubled all floor joists in the area. I put crossbracing with hurricane plates every 12 inches. Then I packed the whole floor with insulation and covered the underside with 2x12 boards. then I bricked up to the floor from the ground and pounded shims in to make it tight.