Wiring 2 subs in parallel:

+ of SUB1 to + of SUB2...connected to + of amp.
- of SUB1 to - of SUB2...connected to - of amp.

With your box you can do it two ways. Do it inside of the box. That will require you to drill a hole in the divider, and run a speaker wire between the two subs. If you want you can seal that hole with some caulk, but it might not be needed since it is a sealed enclosure anyway. Then from where, have one side be connected to a terminal, then to the amp.

Or you can do this outside of the box. This will require you to have 2 terminal cups, one for each sub. Connect the subs together on the outside. From either of the terminal cups, run it to an amp.