Yes, we can't remove any more letters - the preamble ensures there will be 40 letters in the silver zone on completion. But the title tells us that something sheltering in row 5 must be eradicated - and this could be achieved by moving letters within the silver zone or changing some of them. I've been playing around with these possibilities, off and on, but I'm beginning to think I'm wasting my time.
What keeps me going is the belief that it should be possible - the silver zone is messy as it stands, and could use some realignment (and three key letters are already in alignment - two of them attached to the longest down entries, words that really can't be changed). It's easily possible to make the silver zone a better representation of the 'five-word subtitle' - but none of my attempts left 'real words' throughout the grid.
What really puts me off is the phrasing of the 'Instructions' - especially, 'Leaving real words' because there isn't any chance of achieving that with the across entries starting in rows 5 and 6, and I think I'm losing faith in the challenge (and if the solution contains any non-words - the 'Instructions' are inadequate).