A few of us, led by @MudRunnerTD, have utilised old rear seat frames that mount to the existing points in the car, then put the plate you show welded to the frame. This gives you an air gap under the fridge for further storage and opens up the range of mounting concepts. I would use a thimble with a threaded male extension - can get them at Bunnings for a couple of dollars each - I think the M8 units are rated at 230kg each point. Simply drill a hole in the sheet steel and bolt them in, nuts accessible as well, rather than on the floor and rubbing holes in the carpet. You should be able to buy an old crappy seat off gumtree and strip the base and back off it, @AB might be able to post up his solution, recently completed. I have platforms made for both sides of the GQ.