What sized tank ya got? I kept mine in the washroom with 2 new trashcans on wheel dollies. One can was to mix salt water. In that one I had a decent sized pump (300gph I think it was) with a vinyl hose attached to it. Kept it running 24/7 to keep the water oxygenated. Temperature wasn't an issue with me since the room was warm enuf. The hose was long enuf to put it over the tank and re-fill it. The second can was for fresh water, which I used to fill my 37g reservoir hooked to my fuge with a ATO. Only made that water once every 2-3 weeks since the reservoir held so much.
I've never been a fan of RO
/ directly into the tank - prolly cause I never tried it, but I think you'd have to hook up a float switch to make it stop and prevent that water disaster you speak about. The JBJ ATO has float switches already. One for the sump/fuge so it pumped when it got low, and the other for the reservoir so it stopped pumping when that level got too low and you don't burn up the pump. I used a maxi-jet 900 for the reservoir.
The salt water was of course for water changes every 2 or 4 weeks, but I'm a believer in having ready made SW
alsways standing by for emergencies.
When I did changes, I'd use the empty FW
can to know when to stop removing water (siphoning) such that it matched the SW
level when I eyeballed the 2.
Later, my wife made me get a third can (no wheels) which stayed in the laundry room and would be used for the washing machine. She hated to see how much waste water was being thrown away when I made water.