Orient your meshes when they are still separate:

[![Join1][1]][1]

Join them with <kbd>Ctrl</kbd> + <kbd>J</kbd>:

[![Join2][2]][2]

Select the whole (joined) mesh in edit mode and select _mesh_ > _Convex Hull_:

[![Join3][3]][3]

Resulting shape:

[![Join4][4]][4]


  [1]: https://i.sstatic.net/FtQf8.png
  [2]: https://i.sstatic.net/D2ggC.png
  [3]: https://i.sstatic.net/VgkAr.png
  [4]: https://i.sstatic.net/MzXrk.png