Hi all,
Whats the highest TDS reading you have had to work with 
Obviously 000 is what you want but there must be the odd occasion of runing out of resin or a problem with the RO system ?
Reason for this question is i have just had a prob with my RO unit and have a tank full of 018 water.
I'd use 18 if I absolutely had to and not be too worried. Why not give it a go on your windows and see if it dries well enough for you to be confident in using it (it's your confidence that matters, as 99.9% of customers won't see it anyway)?
Also, if the tank in your van is half full of 000, then when you top it up from your feeder tank full of 018, it'll be TDS009. Then when you put more in your feeder tank, that'll dilute the stuff in your feeder tank. If you don't have a feeder tank, half enpty the one in your van, top up with 000 water and you'll be back at 009, which will definitely be OK.
I happened upon someone using 072 TDS last summer (he didn't have a meter, so I checked it for him). He'd had no complaints...
Vin