Have you considered burying the water tank? The house I grew up in had a concrete cistern in the basement. The roof gutters fed the cistern and maintained an adequate supply of water 9 months out of the year. If the water level got low during a dry summer Pops would call the water district and they’d send a tank trunk out for a refill.
Might do something like that when we build the real house. Was planning on earth bermed and saw a design one time where they buried tanks in the berm and fed them from the metal roof and I'll definitely be doing a metal roof.
Plan on putting gutters on my high tunnel and filling IBC totes and might put those in the high tunnel where they'll be less apt to freeze.
Only problem with rain water is that it's basically like distilled water in that it has zero minerals. Fine for plants in the ground of course.