I have that giant crinum. Indeed a favorite and a great attention-getting in the landscape, for sure!
In the winter I wrap it up during our infrequent freezes. I know it will die back and return every winter. But I'm impatient and I dont want to have to wait to see it. So I make the effort. IDK where I got the giant 5 foot coffin-like box, but its "useful trash". I keep it in the garage year after year as it almost fits to cover the giant plant perfectly. With the help of bungee cords old bed sheets, Non-LED Christmas lights and plastic bags to protect from rain, that criumun emerges from its winter protection, like a bad hair day. But within hours back in the sunshine, she springs back happy, and unfazed by winter's cold.
I heart this plant!