Hello! I have a strange area under my front entry in my 1988 built house that is causing me trouble from an air sealing/insulation perspective. Its almost like a crawl space but I cannot get to it from the inside to properly deal with it. I have spray foamed as much as possible from the inside basement area but still having cold air come in the first floor above it. When replacing my front door I removed some trim and found some limited access to hopefully help deal with it. See pictures. The void goes down about 2 ft and opens up after the slab stops under the house another 2 ft or so. Would stuffing as much rock wool in there as possible help (it is technically outside but covered from the weather)? How about trying to slide XPS down and against the wall? https://ibb.co/yd2ShB8 https://ibb.co/zsfQgtM I only have about 1" to work with. Any other ideas?

Thermal camera($200) might help you figure out how to seal it by seeing where the cold is coming from. Other then that you are on the right track in my opinion and just blow in insulation.