i don't know much about the dynomat itself, however, i have a basic understanding of the physics behind the vibrations.
The checker board pattern would cover more area however, not more surface area. that seems to be the key. the more surface area covered, the less vibrations. you can have a little hole and that will allow for vibrations and sound loss. doubling it up would benefit, but probably not in a very noticable way. Maybe if you were pushing 150+db then maybe that would help, but your standard set up wouldn't gain that much considering the cost.
like i said, i don't know alot about dynomat, just basic knowledge, so I might be way out in left feild.