Realized when I was checking out your ride that you have it in a 2nd gen site, not that there is anything wrong with that lol. But you need to bring your gen 1.5 over hear for folks to enjoy.
As for the boxes on my roof, I picked them up at wal-mart some time back for 20bucks a pop. They are mounted by bolts through the bottom on aluminum cross bars that I made up.
And certainly not knocking this site, I love it, but you might want to check out a Nissan specific site http://www.cdn-ntc.ca/index_eh.php
It's Canadian, but we have bros/sisters from south of the border as well. Lots of great stuff for our trucks there.
cheers
E