{HEAD ~ Each side rail portion} includes a horizontal wall between {TAIL ~ the inner wall} and the mid wall 
{ HEAD ~ Each side rail portion } includes a horizontal wall between { TAIL ~ the inner wall } and the mid wall
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH