Roof Bars and Box Bundle. This is the best way of being sure the box will be compatible with the bars. We have tested it for you! You can also save money buying them together in just one order. The Junior Easy 420 Litre Roof Box is a sturdy and convenient way to add additional storage space your vehicle. The Junior Easy 420 is made from UV protected Polystyrene and comes in two easy to assemble pieces, this two part box allows us to reduce packaging making the Junior Easy 420 Litre Roof Box better for the environment. Assembly on this roof box takes just seconds requiring two pins to be inserted to fix the hinges.