Yea, no dynamat crap. Too messy and not as effective as people say it is. Plain ol pink fluffy fiberglass is lot better but, your cab is very small(depth wise specifically) especially for a bookshelf speaker. I wouldn't get that paint goo either. Can find very similar local home dept or even Walmart hardware department. They have paint/ spray on rubber as well but, I wouldn't use it for internal enclosure section.
I never tried foam stuff that Marv listed but, it does look good and best option so far. I only ever used plain ol' fiberglass with sometimes combination of fiberfill/pillow stuffing. Never did anything fancy ever with speakers. I know some people fill their enclosures with bags of sand or concrete but, never found point of that either.