http://www.kargomaster.com/bushman.asp
Sorry, I meant 42" x 50" not 48".
Don't even try to search their site for mounting info since the Xterra still isn't listed.
A few other guys have this rack as well (and have had it for a couple years) and have had good luck with them - Schlud, KillerX, etc.
I bought the horizontal Mighty Mounts from a local Washington DC boating company since they are also used to put skies/boats/gear on top of vehicles. Searching for Yakima Mighty Mounts in any search engine should bring some results. Give me a shout if you need more info.