questions on box and ports

[MACnonsence6]

http://cgi.ebay.com/3-Port-Tube-Subwoofer-Sub-Woofer-Speaker-Box-Pro-Audio-/290507280696?pt=LH_DefaultDomain_0&hash=item43a3955138#ht_1426wt_1139

down below it lists what the box would be tuned to depending on cubes and number of ports that size now are those acurate if so im thinking of getting 2 of these ports building a 5 cube box for 2 hifi 12s thats what the specs here call for

http://maxxsonics.net/manuals/hifonics/pdfs/HFi%20Subwoofer%20Manual.pdf

except the port in the ebay link is a tiny bit shorter but eather way if the specs the site lists are correct i think itll work well. now comes my next delema weather or not i can fit a 5 cube box after sub displacement and port displacement."how do i figure out port displacement"in the trunk of my 98 neon with both 12s and both ports facing threw the back seat hatch. ill get dementions tomaro if anyone here knows the relative size of my cars trunk could u lend some insite as to weather or not i could fit a box with the internal cubic feet i need in my trunk. not sure what thickness wood eather lowes only has one size of mdf here and its 30 a sheet so if theres a standered thiickness that lowes carries thats prolly what it is