Yeah, I couldn't find a reservoir that would fit next to my 75 gallon sump under the 180, so I built one myself out of standard 1/4" acrylic. Holds a little over 10 gallons or rodi water, ready to be pumped into the sump. In the summer this reservoir can last anywhere from 7-10 days, in the winter I can get 4-5 days.
Not quite finished with everything yet, but here’s mine (on the left) still haven’t plumbed it in yet, it came from amazon 2.6 gallons. Small yes but I have a smaller tank. Should last a week or two before needing filled. I’m really proud of this new setup I’m building. Cant wait to finish it.