Eternabond for the remaining 25 feet
With a pebbled roof I would test and retest to make sure the tape will fill the pebbles. I suspect there will be little gaps due to that textured surface, and water will be able to slowly seep in. Just one drop of water once per day is enough to cause the trailer roof or wall to rot.
In this case I would use the Lap sealant only. When you do need to remove it and reLap it you can just leave whatever residue is sitting in the low places of the pebble surface and Lap right over it. You will not be able to use a scraper to remove either the Lap sealant or the tape without leaving behind residue in the crevices.