I would give yourself two feet of space between the tub and any other wall - this gives technicians plenty of space to remove all four side panels and service the tub without removing it from it's location.
At least a foot is suggested, but two gives everyone including yourself more space to work around the tub. I personally like to have full access around the tub so I can walk around and condition my cover monthly - but I'm also OCD and my cover has strong UV exposure year round.