Sub enclosure questions

I've been asked to build an enclosure for a friend, but this one has me second guessing myself because I'm not that knowledgable on ported enclosures... He wants to down fire the sub for protection from elements and being hit by something. (Going in a Jeep trail rig) If I use the enclosure design pictured, but move the sub to the bottom and raise the enclosure off the floor will the port still firing out the front of the enclosure create some weird sound issues? Would it be better to just use a down fire sealed enclosure for this application? For reference he is using a Sundown Audio SA12 and this is the enclosure they recommend.

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Sure you can do that. It's done by many. You can also have both the port and sub driver down-firing. It's not an exact science but I would follow several rough guidelines. Raise the enclosure off the floor enough that you a) have not lengthened the port, b) have not reduced the radiating surface area of the sub driver at any point. So that would mean for a 12-inch driver raising the enclosure up by 3 full inches from the peak of the driver surround to the floor after the enclosure sinks into the carpet/pad. Also, make the stand-offs slight enough that the port nor radiating surface area is inhibited/reduced. You can also exit the mouth of the port 90 degrees and to the side surface (still at the very bottom side) without changing the port length.

Okay that's good to hear... I knew I could down fire the port and sub as long as I left enough surface area space, just wasn't sure I could down fire the sub and side fire the port. I may try that... Thanks for the info David!