Mmm, interesting topic...I'm afraid I don't know the name of the R/O, but Roy Harding uses one that can produce water at a rapid rate, it also brings the TFS down very low, far, far lower than the Merlin.
Cost is somewhere around the £400 mark, he has adjusted the waste ratio to 1:1
Hopefully Roy will view this thread and respond as I can only be vague on the details
Though you would have to also source the pre-filters.
Sarill: You only need a pump for an R/O if you have low water pressure.
You will also need a pump if you have a holding tank and have to transfer to your van tank.
Omnipole can supply you with a pump that will deliver 235 litres a minute for a price that is around the £120 mark, or at least it was a few months ago.
You would also need reinforced 1" hose, I would need 30m myself and that would set me back another £57.
At the end of the day, how deep is your pocket?
When I eventually get the van I've been promising myself for the last 10 months I will be cribbing of Roy, the R/O isn't cheap, buts it's d a m n efficient.
Regards,
Ian