There is a nut welded onto one side of the base which will hold the threaded bar to the base. This welded nut does go "down" or against the floor, so you will need to drill a hole or recess large enough for this welded nut to drop into the floor so the entire square base will be flush with the floor. One more hole in the floor won't hurt anymore than the other four to mount the base. I've got one on my boat, and like it alot.
You could try mounting the base plate with the welded nut facing up, but you will probably still have to drill a recess hole for the threaded bar to go down into/thru the floor to make a secure mounting.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.