Leak Proof External Vertical Corners of Trailer

I use Dicor non leveling lap sealant. I scrape any old sealer that I can that is above the seam, and try to remove any that is loose. Apply the Dicor with a calk gun. On large areas I usually use masking tape on both sides, apply the Dicor, smooth with my finger, then remove the tape. The only trouble I have with this method is the sealer is very stringy when removing the tape. In my experience, the stringy stuff is removed after it dries.