12x16 would work very well. I have a 12x16 right now with a 2x6 and an RO "closet" with a pair of tote tanks stacked in one corner and there is no extra space, but it works. A 2x3 would leave plenty of room for a work bench on one side for bottling/etc and seating on the other side. Uses lot of shelves or even a small loft for extra storage if the evaporator is not right in the middle.