I think that if you have 3 layers (it's probably more than that given the age of your trailer), you'd be best off by going down to bare metal. AND, you may find all kinds of interesting colors from another age as you do it!
"SilverLeaf II" (yet to be delivered)
2014 RAM 2500 Laramie 4x4 CC w/6.7L Cummins
WBCCI # 3430-Unit 21