Your really need to find the source of the water intrusion, otherwise fixing it will be temporary. Every screw needs to be checked, slide seals, slide roof, and seams. I have see on this forum that some owners that had a rotted slide floor replaced it by themselves. Stripping the floor out I believe is from the top and I don't think you can just replace a section like in a stick and brick, but I may be wrong. Hopefully one of the owners that have done this job will chime in, but finding the source of the water should be job one. You mentioned that the rot is just below the area of the electrical shore line storage. Have you tried a gentle water spray to see if the leak is from the storage door opening? You may have to run the water for a while to make sure. An unsealed screw or door seal allowing a drop in over time can cause a lot of damage.