Downfire and ports

Im building a down firing box for my ex cab - just wondering if its ok to put the ports also exiting downward on the same face that the subs will be mounted on. -  would it matter if there was a vent or it was pretty much closed off (talking about the space between the subs and the floor)?

If you are down firing the sub there needs to be enough space between the face of the sub and the florr of the truck to allow for the sub to excurd (Move) this way the sub doesnt hit the floor when its playing....And  yesputting the port on the same face of the box as the sub will be fine....

Just make sure that the sub doesnt hit the floor when it plays.....

Yah im going to have it anywhere from 4-5 inches off - the way the back of my cab is theres almost like a step in the back and then it dips down..

Ive seen some downfire boxes not enclosed off, a vent like i said - is there any benefit or maybe disadvantage to this?

If the port opening is facing the floor you have to be sure that the distance from port opening to floor is at least the same as the diameter of the port.  That space is a part of the port's function.  This rule will cause you to consider the distance off the floor as much greater than the limit of the cone excursion.  And I couldn't figure out what you asked in your last question...?

And be sure you are running the signal through a subsonic filter.  That cone would sag wildly if subsonic freqs are allowed to get through.