I've used 20L water containers in oz for more years than I care to remember. Too many memories of pulling it out to dispense and fill. I always take a 1 gallon container as well for actual day to day use/cooking etc. Then dispense from the 20L to the gallon.
Anyhow, a couple of years ago I put together a gravity water filter scheme and would fill a shower bag with water to then filter through a hose into the 20L (no need to remove from the vehicle). Then since I had extra hose found I could easily siphon water into the gallon container. That worked well with no need to juggle the heavy 20L container around.
Then early last year I found a reasonably inexpensive company on the east coast (in oz) that will make custom water bladders exactly the shape/size you want and put fittings where you want them. Decent heavy duty material etc. So, I designed a wooden box (no 'bottom') and had a mate make it for me (since I was in the US and he leaves near my home in Perth AND he's a wood working wizard). The box/bladder was designed to be just over 5" high but sit between the wheel arches of my patrol and sized perfectly for the fridge and some other boxes to sit on top of it.
So, all I lost was 5" of vertical height which actually helps to raise everything up anyway. What I gained was a 70L water storage container that is 'built-in' and out of sight and safe and reasonably 'low' sitting the vehicle. The box bolts down to existing captured nuts (rear seats) so it is secure and not moving anywhere. I then strap the fridge down to the top of the box along with the other storage boxes. So, all nice and safe, nothing moves/rattles etc.
The bladder has an inlet fitting (on the top edge) and an outlet fitting (on the bottom edge). Hoses run in/out of the wood box and I have potable water hoses and valves connected. To make things 'safe', I can just clip the hoses higher than the bladder and nothing can leak even if there's a valve failure. Filling is just a matter of connecting a hose to the fill side or when bush using a 12V pump to transfer water through a filter from a water source. Dispensing is easy, just lower the outlet hose lower than the vehicle and open the valve - straight into a container or into the 1 gallon 'dispenser'.
When water is getting low it's just a matter of parking the vehicle at a slight angle to get the last of the water to flow out of the outlet fitting.
The whole scheme works great and only took about 30 years to stop using 20L containers
Unfortunately I never took any pictures of the setup last visit back to oz when I installed and used it during a 2 week trip to the bush.
cheers,
george.