making a box

hey guys need some major help on this one. just bought a load of lanzar optidrive audio and i am currently installing it all. i have a little boot to play with though and enclosures are difficult.  i was wondering if somebody could help me on some simple questions cheers james.

can i port an inverted box?
where is the best places to lay dynamat to get the required finish?
whats the main difference in porting the boxes and sealing them atm i am runnign 2 mtx 5500 sledges sealed and sound pretty cool. was wondering what the difference in sound was?

thanks for ur time guys!

I don't know about the inverting a ported box which I assume you mean down-firing but I'm pretty sure it is ok to do if the sag of the sub is ok for that.  There's a sag calculator on this site you can check with. 

Lay dynamat over large areas of sheet metal that resonate for best use.  It is not specifically made for rattles but usually helps, it is designed to damp the resonances of the metal actually.

The differences between a ported box and sealed box can be found by doing some searches but aznboi3644 was on the right track except excursion is very large when getting below your port frequency and near your sub's resonant frequency so a sub-sonic filter is usually required to filter out the super low frequencies.  You commented that you had a small trunk as well which is not ported box friendly as they require much larger enclosures so i would say stay with a sealed box.