if you know you have to tighten/adjust it, the easiest way is to take the batteries out, and lay across the stuff, coming in from the aft cabin...
you can "See" it from the nav door...but doubtful that one can reach it, let alone tighten.
Whilst you have the batteries out, I found it best to cycle the scupper through hulls, and to check all the vacuum breaks and plumbing on the starboard side of the engine room, check the steering cables and wiring from the pedastal and in general do it all while you are there.
I found that flipping the mattress up and over, gives you a flat spot to stow the batteries while all this is going on. I have several pieces of carpet and a couple of moving blankets to cover and pad things...