Having uncovered the rusted metal I realize I have my work cut out for me. Over the course of a couple weeks I tore out the lift, metal plating, walls, and insulation. It was an enormous pain.
For one, there were dozens of rusty old bolts holding the old seat brackets and various other components to the metal that all needed to be removed with one person under the vehicle to hold the nut while another in the vehicle cranked away with the socket. I had to unwire the lift which was interesting. I finally succeeded in getting it free and had a buddy help me move it out. It had to way close to 400 pounds. I then set about using a cutting disc on a grinder to cut the dozens of welds used to attach the metal plating to the floor. I finally was able to pull the metal out and was pleasantly surprised to see unrusted factory paint underneath. The plate medal weighed a ton as well – having that and the lift out should make the vehicle considerably lighter and more gas efficient. More grinder and sawzall work removed the struts they welded into the door to support the lift.
I then unscrewed all the siding, removed it, and threw it in my back yard in case I need to use it later for templates. I ripped all the old insulation out being very careful not to inhale any of it.
More grinder cutting to remove the welded cabinet thing they created above the front seats. Another time consuming pain but a necessary one. I needed to be able to see the frame in order to track down leaks.
With the removal phase complete I can see all the rust spots that need attention and hopefully I should be able to track down leaks and get that part figured out as well.