sub travel distance\pressure?

hey guys, im in the process of wanting to build a box, that box will actually fix into another box\housing that is built into my pickup, 

 by building a box style like in this photo,it will slide as is into the box\housing behind the driver seat and the port will face towards the driver seat. 

now, above the subs will obviously be the top of the outer box\housing. a gap will be compensated for sub travel so that the subs wont hit the top of the housing, but would there be any negative effects created by the pressure being made by the subs pushing air against the housing or will there be minimal air being pushed due to its a ported box and majority of the action will be port side?