I am in the middle of doing this on an ATC truck camper shell (very similar to FWC). Plastic tanks made by Ronco are available from several online retailers, I used plasticmart.com.
You will also need a sink, I got the Dometic sink/stove combo. You will need some tank fittings, one for fill (with vent), one for vent, and one for outlet to pump and drain. I bought a “relocation kit” from plasticmart.com that was basically useless, so just go on amazon and get the fittings, e-trailer had the fill hatch with vent…
I used a surflow faucet and 1 gal/min pump, got all the elbows, t’s, and tubing off amazon…
You will need some big hole saws for your drill. The big round access hatch you see in the second photo came with the kit from plasticmart.com and it leaks, but I think west marine sells one that does not leak. I had to seal mine with silicon. Be sure to use food safe parts and silicon sealant. It is doable, but takes time to gather all the parts and figure it all out. There is some 12v wiring for the pump too. And you have to figure out the drain tube and where it exits the camper. Having a water faucet and sink inside the camper is really nice in bad weather.
