Ft Sill huh? Spent my basic and AIT there.....hope to not see that place again!
Pink foam , either 1 or 2 lb cubic ft density, can usually be found in Home Depot or Lowes in the Midwest. Other parts of the country may be harder to find. OUrs is 2" x 4' x 8'. You could use blue foam as well. Both cut about the same, and the weight difference in minimal on a prject this size.