The 2004 2720SL TM I bought last December developed a leak around the ceiling vent fan. It was too cold to be working removing old caulk so I covered the TM with a tarp to prevent further leaking and resolved to check it out come warmer weather.
That day came today. My plan was to completely remove the unit and re-bed it for a long term fix. The hardest part of the job was removing the old caulk gooped on the screws. After pulling the unit I observed that the vinyl base was cracked clean through in 5 places radiating out from the screw holes. Almost all the other screw holes had cracks as well but not completely across like the other 5. See the attached picture. It's obvious that the factory had not pre-drilled the vinyl screw holes and the screws cracked the vinyl.
I bought some 3/4 inch vinyl stock 4 inches wide (the narrowest they had) at Lowes. I cut off 2 pieces 16 inches long as the original, and ripped them 1 1/4 inches wide.
I attached the vinyl to the roof using 3M Marine Adhesive Sealant. Then I mounted the unit to mark the hole locations for pre-drilling. I pre-drilled the holes then laid down RV trailer putty tape recommended to me by a local RV repair business. After installing the unit and replacing the screws, I did an extensive water test and observed no leaks