Choosing blocker rod for chinking in an old hand-hewn poplar log cabin

I am restoring an old, hand hewn poplar log cabin. The logs are about 7-8 inches thick and the space between them is 4-5 inches and at locations 6 inches. They are uneven logs. My concern is if a use round blocker rod, should I use two or cut one in half (for interior and exterior chinking), or is there a better product? Should I glue or mechanically fasten the blocker rod? On that wide of a gap, am I going to have enough stability? I have read everything I can find but nothing really addre