ProFlex or Dicor flexible RV sealant should do the trick around caulked seams on a slide, windows and hatches. Avoid household silicone sealant because it isn't as flexible as those designed for RVs.
The self-leveling lap sealant (Dicor or other brands) is designed for use on the roof.
'18 Rockwood 2109S '17 Silverado 2500HD WT. Hookups? What hookups? Mountains, please.