I like the spray foam idea but protect any place that you don't want the foam because it sticks really well. It's also a little tricky foaming an open space like a corner because the foam wants to drop away from the wall onto the floor. I'd start at the bottom and work my way up. You could practice on a cardboard box.
Dick_B
2003 SunnyBrook 27FKS
2011 3/4 T Chevrolet Suburban
Equal-i-zer Hitch
One wife, two electric bikes (both Currie Tech Path+ models)