It's important to pay close attention to these openings, as they are thoughts for water rain and snow. For Ideal treatment of a check:
Thoroughly clean the inside surfaces of checks (where the caulk will be in contact to remove dirt and unsound wood.
Apply backer rod to checks 1/4" or wider before staining and caulking.
Stain the wall with a stain that is compatible with your caulking or chinking, making sure the stain seeps into the check.
Gun the caulking into the check - Log Builder or Conceal are ideal for this application.
Tool the caulk to ensure good adhesion to the wood.