I beveled the edges of the cracks on both sides, this would enable the filling materials to get underneath the crack and have something to hold on to. I backed the cracks with simple masking tape and filled the cracks with Great Stuff, insulating foam sealant, available at Ace Hardware of course.
Here's a picture of the cracks after I sliced down the foam and the materials I used. I was concerned with all the voids in the foam. I had expected something solid but realized all those open holes would provide an excellent base for the SEM plasticized bumper repair which was applied next. I had to apply two coats of the bumper repair plastic. It was easy to work with and feather edged nicely.
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