I had that problem. Went through around 10 tanks in a pretty short time span. Tried an alloy tank, but with a screw top, it's more of a pain than it's worth. No matter how much locktite I put on the mounting screws, they would rattle loose as well.
To find a better tank of the same capacity that will fit in the stock location may not be doable. But if you move stuff around on the chassis, you can put a tank up in the right corner where the receiver sits.
It's actually just a new era 3 point roll bar. The 3rd leg makes it very solid. I ran that thing for a very long time and never bent or tweaked it. Many high roof top landings.