I re-sealed the rain gutter areas on my 23B recently and used Geocel Pro-Flex around all the screw heads that were exposed.
Pro-Flex is one the easiest caulks I've ever used in my life. The other one was Dimeric (sp ?) two part epoxy caulk. We tooled it with kerosene and the open cell packing foam material that was cut into a wedge shape. Pro-Flex, a small cup of mineral spirits and your fingertip is all you need for professional results. I swear by the stuff!!
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.