Removing the old stuff is not only better for the tape to stick, it will also look 100% better. I removed all of my caulking on both the front and rear caps of my pr4evious coach and put down a single strip of eternabond tape on each. Looks factory, in fact, looks better than factory and seals much better. I also did this to the skylight.
I removed ALL caulking and cleaned the surface with acetone.
Ron
Ron & Sandie
2013 Tiffin Phaeton 42LH Cummins ISL 400hp
Toad: 2011 GMC Terrain SLT2
Tow Bar: Sterling AT
Toad Brakes: Unified by U.S. Gear
TPMS: Pressure Pro
Member of: GS, FMCA, Allegro
RETIRED!! How sweet it is....