A clean cush(ion) for your tush...
Our situation was not probably the same as yours, but....
When we bought our '88 boat in '94, it had been sitting unused for 3 years and the interior had grown mold and mildew on all the cushions. It was gross...
At first we called some local upholsterers and tried their advice which was to have the cushions "laundered" and then air-dried. This made them look better, but the smell never went away. I finally did what I should have done in the first place and took off the covers -- the foam was visibly shot through with black mold. Threw away the foam and then washed the covers twice, gentle cycle, cold water, with a bit of bleach and soap and air-dried them at home. Another washing might have been better, but I could see that the stitching would not take another washing....
With new "2.6" density foam, they have been great for sitting and sleeping ever since. I should add that each piece of new foam was wrapped with dacron batting which really makes for a nice look and feel. The settee seats and back pieces are tufted, and a local shop re-tufted these. The smell still lingered a bit in the fabric, so I tried "Fabreese" which turned out to be perfume in a bottle and mostly just a scam... and then we used our old ozonator machine for several days and several different months and after a few years the smell is gone.
Reason for this cleaning hassle was that the original fabric was (and still is) in excellent condition and looks really great. This is the dark blue velour-looking stuff that Ericson used in all their boats in the mid-to-late 80's.
I should note that the original zipper pulls on the back side of each cushion were mostly corroded away. Salt air was not kind to them while the boat sat closed up...
We "prevailed" but only through considerable time and in spite of some false starts....
Best,
Loren in PDX
'88 Olson 34