To start with ya guna need about 4 ibc tanks
First tank is going to be filled with normal water from ( ?? Say ur van ) this tank will need a pump on it to push it through the RO ( as said above there will be waste ) and the good water into the second tank, ( I would be having a di bottle just before tank and after RO this will mean tank 2,3 & 4 can be filled with pure ready to go
The slowest part will be filling the first tank but everything else is good to go,
I have a similar situation, as there is a nice secure unit with no power or water that I want, if I don't get water supply fitted I will do the above only I will use a long hose from an outside tap about 50m away 😄
Smudger has posted some pics in past of his ibc setup in his unit but he has water supply, but for you and I with having no power we cant use a transfer pump so a frame of some sort or stack ibc on top of each other with a 2" hose on outlet, ( in theory you just draining the ibc into your van.) would make life easier and it won't tank long to swap water over to van