Regarding the tank mounting, there should also be a couple of rubber bumpers that mount in the side-facing holes in the bumper holder below the top pipe (I don't know what else to call it that can be said here). On mine (2.5 US Gallons, I think), the studs on the bottom of the tank line up with the bottom holes in the bumper holder so that the tank vibration stabilizer runs through those bottom holes. By using steel tub to make the stabilizer it centers through the holes without having to worry about contact with the bumper holder. See the photo. I also found that the bumpers I bought were too thick to fit in the tank tunnel and I could not, safely, press the tank over the bumpers. In the photo you will see where I sliced off some of the thickness of the bumpers and they now fit fine.
I don't know if the tank stabiling bar is supposed to go through the bumper holder, but that was the only thing that worked for me. I suspect I will soon know the truth from one of the friendly folks on this forum.
Richard