i found that plywood left grain marks in the track and didnt give it a realistic look
then i found some plaster board in my garage(hard wall, i think)
i then screwed this to the ply wood so it would'nt crack and break.the paint adheares really well to the surface as its like card
sa for barriers i havn't got that far yet. but on my previous track i used garden hose. it servrd it pupose but it looked really poor quality and rushed i think now im going to use cardboard very thick cardboard.