The initial question I was responding to was something to place the batteries on to isolate some of the vibration from travel so it doesn't reach the batteries as much. I wasn't thinking about space the individual cells with the mat material. I haven't decided yet if I'll find something thin to put between the batteries that still permits the use of the supplied bus bars for interconnect or whether I'll use built cables for that purpose.
I don't know how much you can isolate the batteries from the vibration that the rest of the vehicle gets. The batteries need to be securely fastened down to ensure they don't move should there be abrupt changes in motion (emergency braking, big potholes, etc.). That connection to the vehicle is going to transfer vibration.