This is the humidifier that I use. It works really well and it’s reasonably priced. Air Innovations MH-901DA High... https://www.amazon.com/dp/B077MLKCYW?ref=ppx_pop_mob_ap_share
So don't do this with bottom fill style humidifiers, unless you know what you're doing. Those work differently than the top fill.
Very simple, I put a tee in my ro line. The float valve comes with water line, shut off, tee, 90°, some other stuff.
Drill about a 9/16 hole, then use a file or hacksaw blade to cut in the keyed notch.
I should have installed it lower, so it doesn't have to sit completely full...