Many of the vertical seams on the exterior of my Class C have accumulated black "gunk" from years on the road. In a few locations it looks like there's some gaps which need to be filled. My plan...
DO NOT USE SILICON, do not even walk by your RV with silicone in your hand!
For vertical seams I like OSI Quad available Home Depot, lowes and such, a solvent based caulk, similar to Dicor but much cheaper. For large areas on roof I like Dicor self leveling lap sealant.
There are bunches of Videos on line about sealing an RV, worth the time to look at a few. Jim