Wouldn't it be cool to create a blueprint specifically designed to create rubber trees. It would make getting rubber more efficient later in the game. My proposed recipe would no be cheap by any means though, for it would require 8 rubber tree saplings. The result would be a large pocket of densely spaced rubber trees.
Recipe
S S S
S T S
S S S
(S=Rubber tree sapling; T=empty TFBP)
best of luck