It can be done... but do you really want to put that much money and effort into it? I also hope you have a large weather proof area to work in, along with the skill set.
To get to the wall around the slide you will have to pull it completely out. I have rebuilt a variety of RV's over the years, including wood framed, composite wall, Airstreams and Avions. Even had my hands on a steel framed monster from the 1940's.
I would take the time to do a serious full analysis of just what has to be done. You may be ahead of the game to cut your losses and buy something in better shape, or if you really want to spend a large chunk of your time and money on something you can never recoup the cost of... go for it.
I have gotten away from the RV rebuilding and major repair, I have limited time and would rather spend it camping than working on the camper.