Neither......
Use EternaBond Tape. It comes in several different widths and lengths depending on your needs. Here is one example....
https://www.amazon.com/Roof-Seal-RS-...s%2C296&sr=8-9
As preventative maintenance I put Eternabond Tape over every seam, joint, vent, ladder mount, antenna, etc. on the roof when I get a coach. Otherwise you are inspecting and then adding / replacing Dicor every 3 - 6 months. I only go up on the roof once a year now to clean the roof.