I'm kinda wondering why work so hard to get ALL of the stuff off. I would think chipping it out in chunks, followed by some scraping with a putty knife followed my some wire brushing, then the good ol' shop vac and you'd be good to go. It is after all, storage. If nothing else, sealing in the bits down in the weave may be a reason to put some tough paint on with a brush. I think the real issue for me would be to keep from breathing the foam dust and the paint, if you use it in such a confined space.
The chemicals listed are, at least for me, nothing I'd want to work with unless I and the whole project was open to outdoors, period. I've removed a lot of sloppy spray foam applications...by me...over the years, and the mechanical removal is the safest. As to sealing the little bits left in the weave with paint? That would be up to how "Monkish" you are. "Monkish," as in the television series, Monk.
Oh, gasoline works really well for removing the stuff. I have a red neck friend who tried that...once.