Retrofitting tanks on a vintage 1957 Wanderer

I am doing a shell off restoration/renovation on a 1957 Wanderer Custom. I have taken the shell and subfloor off, and have sandblaster the trailer and applied POR15 to the trailer. I want to purchase a new fresh water tank, gray water, and black water tank. I am having a hard time figuring out where and what size inlet and outlet openings to install. Does anyone have any suggestions. The black tank is the 8 gallon, and the gray tank is 16 gallon, 50 x 21 x 4. The fresh water tank would be 40 x 12 x 10 and would fit where the old metal tank was under the gaucho couch in the front. It has an angled fill valve on the exterior of the Wanderer, about 1/3 of the way up the front curb-side panel.
Having never done anything like this, I am in way over my head! If anyone knows of someone who works on vintage Airstreams in my area (LaGrange, KY) I would love to hire someone to show me the ropes, or do the work and let me watch and learn. Thanks in advance for ANY help!