a flojet demand pump and a 16 gal ebay water tank i have a water spigot on the driver side of the trailer enough for me and a buddy for 3 days including hot showers from the tankless propane water heater not pictured. it was done on the cheap but works well, if you cant tell im a cheapskate. lol. i never did put a fill port in it, i might some day i just ziptied the fill host to the vent hose and called it a day, i stuff a plastic bag in the hole after filling lol it works.
takes up more room than id like inside the trailer, but id rather not have it outside, dont really have much room outside of it to mount it either.