With only about 10' of drop you want to stay with just 3/16 and run it all the way. What little drop you have and it's vacuum created would be totally lost if you go to a mainline. If in time, you add a conventional vacuum pump, even an old dairy pump a mainline can be advantageous, now, with only a seaflo likely not. Even with the 10', I'd suggest you tap 2-3' higher on the high end, then more vacuum will help counteract the friction loss on the 300' run. With a system like that, I suggest you not have more than 20-25 tap on a single 3/16, and don't combine it or switch to a 5/16 or all gravity vacuum will end where the 5/16 starts.
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.