Anyone know where a good place to find something like this is? Basically I need a 1/2 piece thick sheet that is 10 ft by 18ft or possible two 5 x 9 ft. pieces.
TRY HOBBY LOBBY,MICHAIL'S OR THE RAG-SHOP
You'll have a hard time finding something that size. Look in the Yellow Pages or on the web for a plastic supplier or building materials warehouse. You will probably have to do some calling around.
