A couple of us - Scarps and I - have done it by making a replacement floor panel in the back. Mine is a 19 mm hardwood ply board with tough carpet on the top. It replaces the original floor perfectly.
Here is mine:
The fridge slide is long enough to hold the 40 litre Waeco and the 100 Ah Gel battery in a battery box with a DC-DC charger on top.
It is held down by a ratchet strap which is attached to a new bolt to hold down the spare tyre:
This is the new floor, with a circle of 19 mm ply to reinforce the centre.
The fridge slide and the compressor/air tank are held down with T-nuts into the 19 mm hardwood ply.
When i am going away, I just pull out the original floor, put in the new one and do up the ratchet strap. Then I load the battery, fridge and compressor/air tank and load the rest of the stuff. I use the car seat attachment point to anchor ratchet straps to hold everything down and I added a heavy duty loop near the front otf the fridge slide for the other ends of the ratchet straps.
Cheers
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