The All Stop Disposable Mattress Cover should be opened fully. The bag only opens on one end. You should carefully slip your mattress only inside the bag, making sure that no holes are torn in the process. The box spring does not have to be encased because you are not sleeping directly on the box spring.
Once the mattress is inside the cover, you should use tape of any kind to seal the mattress cover. Make sure to seal the full side and any holes that are in the bag to let air out making a tighter fit and more comfortable sleeping environment. This will make your mattress completely bed bug free.