Energy Seal from Perma Chink is what you want to use for caulking, but I do not recommend filling all of the checks (cracks) in logs unless they are allowing wind, water or bugs to get inside. You should caulk every chink line between each log and around all doors and windows. I would also recommend using Perma Chink Life Line stain and clear coat. Since the exposure to sun and weather is so hard you should re-apply the clear coat every 2 years on that side. If you ever need to apply a light coat of stain it can be applied right over the clear coat.