Hello Barry! Someone has most likely applied an elastomeric roof coating in the past. Usually this is done to a roof with a epdm (rubber) membrane to prolong the life of it and/or stop leaks. As long as the self leveling lap sealant is in good condition on your airstream, there's really no need for application in your particular circumstance. Typically it can be removed with a pressure washer, a putty knife, and some elbow grease. If the lap sealant under it, around the vents, skylights, etc. is cracked, it should definitely be removed and replaced. For that, I recommend a multi-tool with a scraper blade and denatured alcohol. When reapplying the self leveling lap sealant, be cautious around the edges. If applied too heavily, it can run down the side of the airstream.
Hope this helps!
Kelly
The Mobile RV Repair of Flagstaff and Camp Verde