Seal around windows, doors, and lights

I was at a reputable dealer yesterday to get caulk (not camping world). They only had dicor and 100% silicone caulk. I asked them what to use, use dicor for the roof and silicone for windows and doors and everything else. I told him I had read to never use silicone, he disagreed and said they put silicone on all trailers they sell or service. This is a reputable dealer (in OR) that sells a NW brand many rave about. I was very surprised, but purchased the dicor based on this website. Glad I read through these treads. I'm replacing my downspouts and silicone is not the right product...