I have been tasked by my buddy to build him an enclosure to put a pair of low level 15's in his 98 4-door Explorer. I have built plenty of simple, sealed boxes in the past, but want to try my hand at a ported one this time around. The maximum dimensions he gave me to use are 40W x 40L x 13H. That being said, what would most likely be the best configuration for his situation? Speakers up / Port up? Speakers up / Port back? Vertical or horizontal port? Etc. Once again, Thank is advance for any and all opinions.