I empty mine & lay it down in back yard, but that is because I
transport it to my church gym and set it up as a 3rd hoop for a little
3-on-3 bball tourney that we have over the Christmas Holiday. If I
left water in it would be a solid block of ice and could not empty it
for transport.

If I did not have to move it every winter, I think I would fill it with
sand and leave it up year round. I am pretty certain leaving water in
would crack base, but with dry sand, you are good to go all year.