From the bottom of the tank area is a piece of tube coming up. On top of this tube is a piece of 1” v-thread welded through a 1.75x.375 spacer. This threaded rod comes up through the 2x2 stock, and is clamped down with a giant wing-nut type thing.
The tanks are brace at the top at three points on each tank, 2” across, and in roughly a triangle shape for even pressure. I cranked the nut on pretty hard to try and crack them, but couldn’t get them to budge. Some good plastic I guess. The threaded rod is held laterally in place by two braces coming from the two bars going across the back of the chassis.
Still need to cap the ends of the square stock, and put on down tabs for the aluminum tops. Still rolling around in my mind if I want to make a bar going around these tanks in the rear. I think they are safe, but peace of mind is a good thing I guess, better safe than sorry.