Box for BTL 18

Just got my new BTL 18 with all the goodies i wanted. now for the box. I plan on building it, but it will be the first one i build. Naturally i have a few questions that i would appreciate anyone taking the time to answer. I got alot of box building info from http://spkrbox1.spaces.live.com/ it seems to be legitimate information, i'm pretty sure i got the link from this site. but should the height of a box really be 1.4X the weight??? with my calculations, to get a box of 8.6 cubes BEFORE port and sub displacement, my box has the be 34 inches tall!!! (25X34X17.5)

Ports brings me to my next question... are there are any performance differences in the type of port you use? RE has a handy-dandy L-shaped port calculator on their website. I can do the tuning frequency calculations, although i don't particularly like to (i'm thinking about 32Hz... it seems to be the choice among many). So square ports, cylinder shaped ports, L shaped ports, all the other ports... whats the difference?

I don't plan on competing in any competitions. I just want a nice sounding system that hits hard.

one last thing, i should use the thickest MDF i can get my hands on, right??? Would you say minimum of 3/4 inches thick?

Lastly, for real this time, box size constraints based upon my vehicle shouldn't really be a problem. Either going into the back of a Ford Explorer sport, or a 1987 Bronco. I'm not bringing home groceries so i don't care if it takes up the whole back.

Thanks guys!