Well the first thing you should be aware of is that your tank is way to big for an escort van!
I'm not sure, but I've heard it said on the forum that 250l is about the max size you should go for.
You don't need an awful lot of space for a water butt, try getting a garden one, about 300-350l.
The R/O takes up very little space.
I've used WFP for 21 months now, and have so far only used as much as 300l in a single day on only 1 or 2 occasions.
I have seen on Gardiners site that they do submersible pumps at a very reasonable price (a bloody sight cheaper than the place I got an identical one from too
)
Mine pumps out 135l (or is that 125l??) of water a minute, that fills up my tank in no time. Fed through a 1inch hose.
I have to pump it 45m up the garden, and it empties my 350l water butt in about 7 minutes.
My own R/O is much slower than than the Merlin, but it still fills up my water butt every day, but it does have the advantage of producing water prior to going through the DI resin at about 0.000-0.002 ppm on the TDS meter.
I understand that the merlin takes the water down to about 0.015 ppm prior to going through the DI.
Costs me hardly anything at all in resin.
The average semi will use up about 15-20l of water on a regular clean, and the average semi will take you about 10 minutes to clean with WFP.
Cost per litlre will depend on how hard your water is, and how low the Merlin will take the reading down too.
If you are producing about 200l a day, and the water is at 0.015ppm then you'll go through about a litre of resin a week...or at least that was what I was going through when my R/O lost efficiency
My own fault for not flushing the membranes regularly...or not at all for over 12 months
Live and learn though
Ian