You do not want to R.O. ahead unless you can keep the concentrate cold. When you concentrate the sap you also concentrate the micro-organisms and you raise the temperature. Unless you can cool the concentrate down it will spoil quickly. Proctor concentrates to about 35% sugar and cools the concentrate to about 25-26F.
You would need to cool it to just above a temperature when slush starts to form to hold it for a day or 2, less if just holding for a few hours, but it still needs to be cooled or you will lose some sugar and make darker syrup. The exact temp you would need depends on how much you concentrate and how long you will hold it until you boil it.
Another point, would you have power to run an R.O. where you collect the sap, an R.O. is power hungry.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.