Attachment 160465
An 8mm eyebolt into the preinstalled nutserts in the end of the tank, plus an 80kg Velcro strap around the seat mount. One of these on each end, plus the front seats pushed right back against it, and it does not move an inch!
If I lift the side of the tank, I end up lifting the whole side of the disco.
I'm going to call it secured.

