The floor in the boot of my mondeo estate was too rusty to bolt tank into so have used ratchet straps with bits of timber under the floor to spread the load. Also got some of that blue rope off the BT guys and tied the front of the tank and my barrells to the seat belt points. Think it will be ok as can never get kids to wear their belts anyway. Had to put the spare wheel on the back seat now though so with the barrells they are well wedged in anyway.
Will try and post some piccys later.