Insulation, Radiant and Vapor Barriers - insulating small t&g cedar (ceiling - wall ) voids, what should I use

I have a cedar home. there is no attic space. The cedar ceiling continues from inside the house to the outside and provides the outside overhang. I can see light through these voids at night if the lights are on in the house. My heat loss is bad. I calked and painted 3 years ago and the calk has shrunk. the voids are open again. I cannot use the canned foam insulation as this would make a terible mess. The walls are about 5 inches thick as is the length of each void.

I thought about takeing small peices of r13 packing each hole and then installing a couple of the soft orange ear plugs, installing all materials from the inside. (The voids are all a little different in size.) The voids would then be plugged and I would not make a mess of the beutiful fiinish of my ceiling or the top of walls. I am open to all ideas, please let me know.
Thank's
Millmnt