Upgrade the membranes to 150's and add another to make it a 450gpd r.o
450gpd still isnt the best for a van mount, if possible can you make it into a static system?
(Ibc in shed and produce water into it while working/over night, then transfer water over when needed)
Aquatec 8800 is a good booster pump
(I would post this in the WINDOW CLEANING section if you want help mate)