The tank is 6 tall, so to secure it I built a box. I ripped a piece of 1x8 pvc trimboard down to 6 wide to build it with.
Then I drilled holes around the lip of the tank to secure it to the box with stainless screws.
I did this before opening the trailer. Once I removed the old toilet i realized I was going to have to modify. The discharge on the tank was located 3/4 closer to the frame rail in the trailer and 2 toward the tub from the hole in the floor. The 2 would be easy to trim off the existing hole but the 3/4 would put it on the trailer frame. Luckily the mounting flange on the tank is 1-1/4, so I was able to trim off 3/4 from the back side.
Now I had to modify the box I built for the shortened back flange AND for the wheelwell interference I didnt anticipate.