1989 Malibu skier floor problems

I have a 1989 Malibu skier, I have outfitted it with sacs, tower, etc and am very happy with it's wake. But I have a few soft spots in my floor. Can any one tell me what may be causing it, and how hard it is to replace? they only exsist on the passenger side, and we are not sure if they are coming from water getting in the vent tubes, the fat sacs leaking, or from the previous owner not pulling the center plug? possibly a bilge not working? please advise.

If you have a few soft spots, then it is time to replace the whole floor. I own a '92 Sunsetter. My first season with the boat was the summer of '02. To make a long story short, by August I had a hole in the floor in front of the ski locker. If you are handy and have a compressor, Die grinder, and some other needed tools, you can do it yourself. Otherwise it is about a $3,000 job. Chances are it is not the fat sacks, just exposure to water over the life of the boat.

Because its an 89, the boat was made with wood. Over time, wood rots when there is enough exposure to water. This is why boats are now made of all fiberglass. It looks like Doug is speaking from experience, so I'd follow his advice