One side or both sides of {HEAD ~ the panel} 20′″ may be covered with {TAIL ~ a layer}, such as an outer covering layer 
One side or both sides of { HEAD ~ the panel } 20′″ may be covered with { TAIL ~ a layer } , such as an outer covering layer
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH