All you need do is research ibc tanks local to you. I purchased a black ibc tank for £40. I wanted black as it was going to be stored outside and so the sun will not negatively affect it.
I currently use a 450 gpd ro unit with a small 100 psi booster pump from china and it takes roughly 24 hrs to fill the 1000ltr ibc from empty, so i dont let it drain before im refilling.
Then its a submersible pump inside to transfer to the van tank.
I use a sedimemt filter first followed by a fibredyen and then booster pump into the membranes which i replace roughly every 2 yrs or so (membranes)
Yet i back flush every time for five mins before I fill the tank up, to help relong the life of the membranes.
(A vid on my channel,,,,,as an idea
https://youtu.be/EpqWaagulfQ )