Windows etc can have a foam seal or butyl putty tape. If there is squeeze out over the summer (common with butyl) then using a plastic scraper and carefully clean the squeeze out back to a sharp edge. Then, using the correct product apply a small bead around the edges. Remember if your doing windows only do the top and sides. Leave the botton unsealed to allow any moisture thst might by a place to drain out.
Most people say either Dicor or Proflex for RV caulking choirs. Tried Proflex once. Hated it, so I always use Dicor. Remember there are two Dicor products. Use the correct one. For roof seams lota of people swear by eternabond. Roll it on once, seal the edges and its done for years.