EternaBond
Just bought a roll last month after returning from our spring trip. Discovered that when the dealer put a new end cap on our Hi-Lo, they didn't do a good job. Too few screws were used to secure it on the roof, causing gaps that in turn caused the caulking to separate from the roof, so, after reading a lot about it, I put EternaBond on the seam. I cleaned the aluminum roof with a good cleaner (as recommended by manufacturer) and the tape stuck like a magnet to it and the PVC end cap. I did put a line of caulking on the leading edge as recommended.
Since I was trying to beat the approaching rain, I haven't applied it elsewhere on the roof. The tape is pricey, but if it lasts as advertised, it'll be worth it. I will check e-bay and Amazon to see if it's cheaper. BTW, our trailer is covered (CalMark custom RV covers) so the tape won't get the full northwest weather effects while in storage.
Frank