Anyone know how to safely remove a previous coat off roof?

Without photos it's difficult to advise what you should do. Since it's an 88 the repair needs to be inexpensive due to the low resale value of the RV.

Based on what you describe I would cut away or pull off any loose patching material. Clean the entire roof and make sure it is dry. I would use eternabond tape to seal all seams and tears and then use Eternabond sealant to coat the roof. See this website for more info
http://www.eternabond.com/RV-Leak-Repair-Products-s/22.htm