I am considering my options for both fresh and grey water capacity for my build. I will not have a black tank. I plan on having the fresh water tank in the interior of the trailer and would like to fit my grey water tank under the trailer. It seems options are somewhat limited for tanks that would fit between the floor framing (16 inches). I have considered possibly sistering two separate grey tanks together to expand capacity. Looking for others ideas/experiences as well as recommended capacity.