I'm aiming to seal the gaps around the trim pieces (door trim, window trim, baseboards) that are on the exterior walls of our house (>100 years old). Seal out the wind this winter. :-)

In examining some of the rooms, I noticed that at some of the interior corners, the perpendicular baseboards don't meet evenly and have gaps. Some of the largest gaps are 3/16 inch wide.

My "newbie" questions:

My tube of Dap Alex Plus caulk says that it should not be used for filling "butt joints". Would such corners where the baseboards meet up be considered "butt joints"?

I'm not sure how deep these gaps go. I mean, the baseboards seem to be about 1 inch thick when I try to measure them from the painted wall portion. So, wouldn't that mean the gaps could be 1 inch deep?

My Dap tube says to use a backer rod if the gap is more than 1/2 inch deep. How would I use a backer rod in this situation? Stuff it into the gap as deep as possible, and then caulk the gap in front of the backer rod?

Is there a 'best practice' to seal these gaps between baseboards at interior corners that I should follow?

Any advice will be greatly appreciated!

Thanks in advance,

Lee