I just did a fair amount of research because I need to re-caulk pretty much all of our 9 year old Mobile Suites. I have always used Dicor self-leveling on the roof and it is the best. I tried it on horizontal and vertical seams on the side and I didn't like the outcome. -More research.- Decided to try Geocel 28100V Pro Flex Crystal Clear RV Flexible Sealant. This stuff works great and looks good when done. I'm scraping the old off some of the seams and just cleaning and applying fresh on some depending on the existing condition.
Method: Scrape using sharpened plexiglass (optional), clean with denatured alcohol, mask with blue masking tape, apply new sealant (I bought a pneumatic caulk gun $25, and worth it), smooth using FixtureDisplays 3-IN-1 Caulk Tool, remove tape as soon as possible (before the sealant skins over). Two people works best. One applies material, second comes right behind and smoothes, first person pulls tape behind the smoother.
Sorry for bloviating, hope it helps someone.