I had a horrible time with duct tape glue, some black tar type stuff and some gooey white sticky stuff the previous owner tried to cover seams and stick on seam tape with. After trying many products I purchased goof off - originally got it at the paint
store but I think you can get it anywhere as I have since seen it at home depot. It is far more powerful than goo gone and much different. Will remove just about anything (they even warn it will remove the glue under carpet if not careful!).
Anyhow...not sure if this will work for you but I was pleased with the results removing all the yucky stuff from my trailer.