The Heater Xtender 48 ft Home Batting Cage definitely contains everything you need. It is a COMPLETE batting cage, which includes the poles, net and frame. The only thing you might want to add is an L-Screen or any other type of screen designed to protect a pitching machine, since it will be sitting inside the cage.
The outside netting is already more or less "sealed". There is a very small hole in it which allows a Heater pitching machine to be attached on the outside of the cage via the batting cage harnesses that come with all Heater pitching machines.
We have included a tab on the product page that shows the owners manual and assembly instructions. You will see that if you did want to extend it to a longer cage, you would have to cut away the net where it attaches to the other cage. Otherwise, it is a sealed net other than the aforementioned small opening for the pitching machine harness for Heater pitching machines. If you have any other questions, please don't hesitate to call us!