I am not sure about an SUV but subs up port up does not sound horrible in a hatchback. Actually it sounds pretty damn good and tends to get very loud in certain vehicles. A lot of Euro hatches do subs up port up and are super fucking loud!!! Anyway like I said I am not sure about doing both subs and port up in an SUV, but from personal experience sub up and port firing diagonal back into the corner of the hatch works very well for a single sub setup.
The most recent SUV build that I did was a dual 15 box with a single 10" aeroport. The box was 5.5 cubes after displacement with 2 Crossfire XSPL V1 dual 1.4 ohm 15's. They were wired down to .35 ohms on a Sundown SCV3000D. The box was tuned to 47hz for SPL, however, would play over a 148 from 32-55hz. That is pretty damn cool if you ask me. It was an SPL box, but for some crazy reason was one of the absolute best sounding enclosures that I have ever built. Others that heard the box had no idea it was intended for SPL and not SQL. The best number that it put up was a 150.5 on the dash sealed with maybe 2200 watts after impedance rise. If we would have added more port area it would have probably helped to keep the rise down as well as increase the SPL due to more port area and the result of higher tuning. This more than likely would have killed any of the sound quality potential, and I say sound quality with the slightest amount of seriousness in my statement.
If there is any interest in seeing the setup, it isn't pretty, let me know and I'll throw up a few pics that I snapped of it. It's not my build , but I did build the enclosure and do the box design. The setup is going to change to 2 Sundown ZV3 18's or quite possibly even 4 ZV3 18's ran off of a ton of power. The amplifier configuration isn't set in stone yet but will probably be a pair of Sundown SCV6000D's, SCV7500D's, or even a pair of NS2's when they are released.