I don't think it is that uncommon no air circulation. Just make sure to get someone that is good at glass work and cover every thing in cabin or you will know it every time you set in the cabin. You need a strong vac. so it will draw the dust out while they are working in cabin V- berth. I don't know that you would have to replace the whole sheet, would have to let tech look at it. Make sure it is all glassed in and drains put back in. I don't think it would be a problem if fixed right. When stored I think you should open those compartments under V-berth pad so the air can circulate, some people stuff them with things that hold moisture and that is what I believe causes the rot that you have.
Hope this helps